Such an unwieldy weapon that you're describing would've been picked apart quite easily, either by the light troops that would've capitalized on its slow movement and poor mobility and swarmed it or by simple maneuvering of the formation. The idea of the "phalanx" is erroneous, particularly the misconception of all such tightly packed infantry formations as slow and cumbersome. What a "phalanx" is actually has nothing to do with the weaponry. The Greek word phalanx means "stacks"--one could translate it as columns, or ranks. It's the normal linguistic method in Greek of signifying an orderly formation of ranks and files, particularly of infantry. In normal Greek usage it's by no means restricted to a particular type of soldier (e.g. hoplites)--for example, the Romans are described as forming their infantry in phalanxes, i.e. ranks, and even the barbarian Carthaginians and Persians do as well (incidentally, in Homer the Trojans do not. The use of orderly infantry, which during the late Dark Age was only beginning to be widely used in Greece, seems to be unknown to them, which is one of the main indications that such tactics, at least at first, were regarded as something that separated Greeks from easterners). And if we're going to use phalanx to describe a specific type of formation, it is used as a technical term to describe only the formations employed following the introduction of novel tactics by the Theban general Epaminondas (usually with a capital P). It is still used as a sort of shorthand by classicists (it's rather cumbersome to constantly have to say hoplite formation, or heavy infantry ranks or something like that) but this of course leads to confusion among many readers who come to believe that the word describes some very specific tactical formation, when in fact it's nothing more than a method of saying ranks.

Anyway, I digress. The point of that is that many such heavy infantry formations were quite mobile. I'm using the word the way many classicists do informally, to mean both phalangite and hoplite formations, and similar formations closely modeled on them. Hoplites in particular were actually quite mobile if they wanted to be (just consider Athens' marine force) and were perfectly capable of performing complex maneuvers very rapidly (Xenophon is rather fond of describing them). In fact, this is one thing that made the hoplite so successful, that he was (at the time of his introduction) the most heavily armed infantryman in the world and possessed mobility and flexibility unparalleled for quite some time by any heavy infantry force in the world. Phalangites of course were a bit different, relying on other forces to deal with mobility and essentially acting as a heavy backbone. Still, their screen of light infantry is repeatedly credited with causing major trouble to attempts to disrupt the formation through head-on attacks.

Now, this is not to say that specialty weapons were never used to try to counter such formations. Most obvious is the use of elephants, which have something of a mixed record. When used properly they were fearsome weapons and could plow through a formation. All too often, however, they were committed to frontal assaults and failed to penetrate pike walls or fell victim to Alexander's method of opening the ranks to their attacks. And in flank attacks, where they excelled, they were often too slow and cumbersome, falling prey to harassing attacks by more mobile troops and panicking.

The scythed chariots of Darius III, later copied by Mithridates, also come to mind. These chariots were heavily armored and covered in blades and all sorts of nastiness. In addition, Arrian says that the charioteers were well armored. Unfortunately these met the same fate as the elephants, but with even less effectiveness. At Gaugamela where they were introduced they were massacred in a frontal assault, unable to breach the pike-wall (contrary to Darius' expectations) or (once again) falling victim to opened ranks. Mithridates used them slightly more effectively, since the Romans had no buffer of pikes, but Roman drill and discipline shut them down fairly quickly, since it's awfully difficult for a mobile force like that to plough through tightly-packed and well-disciplined infantry, no matter how many pointy objects you stick on it.

The problem with thinking of vehicles back then like vehicles now is that back then they couldn't have moved faster than people walking. Even if you could make a fully functional medieval tank, I can't help but think it would be rendered irrelevant by the enemies just walking away/around after killing the exposed oxen.

The closest thing I could think of would be the Hussite Tabor, which was essentially circling armored wagons to create a temporary fortification. Defenders could then pour ranged fire upon foes while guarding a relatively small number of gaps while opponents would have to break formation to get into melee range. Although, this was normally a technique used to counter cavalry charges more than massed infantry. (The Hussite Wars by Francis Lützow (hrabě))