I'd like to add a bit more to my previous answer, as I feel I could go into a bit more depth on some of your questions. Therefore, this answer will delve a little more into the years before the fall of Philadelphia, what life was like surrounded by Turkish emirates, and how the city was able to last so long as an enclave.

In the 1290s, the Byzantines still held substantial lands within Anatolia. These possessions had definitely been reduced by the rise of the Turkish emirates, but were still significant enough that Andronikos II, the Byzantine emperor, committed substantial efforts to fortifying the empire's defenses here. Some historians, such as Savvas Kyriakidis, argue that these investments setup Byzantium for a purely defensive war with the emirates.

This seems to be a reasonable conclusion, as the Byzantines truly struggled to meet the emirates on the battlefield and were hard-pressed to defend their Anatolian possessions, such as Philadelphia. In fact, as the Byzantines struggled to even raise substantial armies during this period, the defense of these cities primarily came down to local governors. These local governors, faced with increasing challenges and lack of support from the empire, usually carried out their own diplomacy.

For example, by 1306, we have evidence of Byzantine cities in Anatolia allying with, marrying off their daughters to, and warring with individual Turkish emirates.^(1) What we should see these cities as are semi-autonomous states, who through their limited support from Constantinople, instead decided on their own course of action. Often, this course lead them to working with the emirates, as they felt Constantinople could no longer properly support them.

To see this in action, we should look at Philadelpha in 1310. The Germiyan emirate had laid siege to Philadelphia and the defense efforts seem to have been lead by a local bishop, Theoleptos of Philadelphia. Theoleptos had asked for help from Constantinople, but had been denied.^(2) The following spring, he worked out a peace treaty with the emirate. In exchange for food and other supplies, Philadelphia would become a tributary of the Germiyan emirate.^(3)

Similarly, in 1304, where Philadelphia was also besieged, Constantinople had failed to adequately defend their Anatolian territories. The only saving grace of 1304 for Philadelphia was the arrival of the Catalan Company. The Catalans, a Latin mercenary company, was widely regarded as one of the preeminent fighting forces in the region, as the contemporary Byzantine Gregoras says:

The enemy seeing the well-ordered march of the Latins, the splendour of their weapons and their unmoved eagerness, they fled. And they carried themselves away, not only far away from the city but close to the old Roman frontiers. This was the quantity and the quality of that army [the Catalan Grand Company], and it was so exceptionally organised because of the arms, the experience acquired at wars and because of its multitude (alongside the Latins campaigned not only the select of the Romans but also as many as were available from the army of the Alans). And because of these, they [The Catalans] inflicted such terror on the enemy that many said then, that if the emperor’s orders motivated by cowardice did not prevent them from marching further, there would be nothing to prevent all the Roman cities and lands, which were clearly in the hands of the enemy, from being handed to the emperor within a short period of time.^(4)

Here, the city that Gregoras is referring to in the second sentence is Philadelphia itself. The Turkish emirates, seeing that the Catalan Company was soon to arrive, choose to lift the siege instead of meet the disciplined mercenaries on the battlefield.

However, these successes were rather temporary in Anatolia. The Catalan Company proved too expensive to maintain for the nearly bankrupted Byzantines. Instead of paying them, and fearing the company would revolt, the Byzantines murdered Roger de Flor, the leader of the company, and slaughter many of the mercenaries accompanying him at the time. So the Catalans, one of the best Byzantine answers to the Turkish emirates around Philadelphia, had been brought off the table.

Perhaps the most significant support that Philadelphia received during this time was the granting of pronoia to soldiers. These were land and other grants, that the Byzantines believed could embolden their soldiers to fight harder. Following the logic that a soldier is more likely to fighting for land that he technically owns, the Byzantines granted an extensive number of soldiers around Philadelphia land.^(5)

From the early 1320s to 1340, we have more accounts of wars and battles around Philadelphia, but nothing as significant the two aforementioned events in 1304 and 1310. Perhaps the most significant development for Philadelphia during this period was a general alliance with the emirates of Saruhan and Aydin, which were near Philadelphia. These emirates helped the Byzantines in several wars and aided the capture of many islands in the Aegean. Therefore, these alliances may account for a somewhat calmer period for Philadelphia.

From 1341 to 1347, these emirates were also involved in the winning side of the Byzantine civil war. Even the Ottomans aided Kantakouzenos, who would eventually seized the Byzantine crown. In somewhat of an alliance with the Byzantines, these neighboring emirates may have had little cause for conflict with Philadelphia. However, the historical narrative for Philadelphia during the civil war is rather sparse. But we do know they continued to be a part of Byzantium after the war, so it may have been relatively untouched.

Kantakouzenos, who was supported by the Turkish emirates, was rather unwilling to challenge them for their dominance of Anatolia. Saying "In terms of military experience they [the Turkish emirates] are not inferior to the Byzantines, but instead are far superior to them in terms of numbers, more vigorous in their preparations for war, better prepared and readier to campaign than the Byzantines." Kantakouzenos followed a policy of diplomacy, friendship, and appeasement with the Turks.^(6)

A mere 15 years later in 1362, the Byzantines, along with Philadelphia, became a vassal of the Ottoman Empire. Therefore, these cities would have generally been granted protection or aid by the sultan. The Ottomans remained relatively unchallenged in Anatolia, which generally granted the Anatolian cities some safety, until the arrival of Timur in 1402.

Finally, from 1378 to 1390, Philadelphia technically was supposed to be a part of the Ottoman Empire, but had to be enforced in 1390. A more thorough account of this can be found in my previous answer, which I believe you may have already read.

As we can see, Philadelphia was a rather adaptive city. While technically under the Byzantines, Philadelphia soon found itself semi-independent. As a distant outpost of the Byzantine Empire, the Philadelphians often found themselves at odds with various enemies. Unable to get much support from Constantinople, the city forged it own diplomacy with the emirates. Warring with, allying, and marrying into important Turkish families, Philadelphia proved to be resilient for over one-hundred years.

Bibliography

^(1) Kyriakidis's Warfare in Late Byzantium, 1204-1453, see page 29.

^(2) The Twilight of Byzantium, see page 34 in Hero's chapter "Theoleptos of Philadelphia."

^(3) Encyclopedia of Islam: Volume II, see col. 989.

^(4) Kyriakidis's Warfare in Late Byzantium, 1204-1453, see page 132.

^(5) Kyriakidis's Warfare in Late Byzantium, 1204-1453, see page 132. Also see Bartusis' Land and Privilege in Byzantium: The Institution of Pronoia, see page 75.

^(6) Kyriakidis's Warfare in Late Byzantium, 1204-1453, see page 39.

u/Snipahar answered a very similar question just a few days ago:

What do we really know about the capture of Philadelphia?