Are there any long form Phoenician written sources, I know for example that there are over 10,000 inscriptions in a stereotypical form (i.e. X son of Y king of Z etc.) but are there any literary sources still extant, even if these were translated to Latin or Greek?
Sort of! A few notable examples:
(1) The Hellenistic writers Menander of Ephesus and Dius produced histories of Tyre using local records; short extracts, mostly from Menander, survive in Josephus' Antiquities and Against Apion. The comparative, external, and onomastic evidence all confirm that Menander, at least, used Phoenician sources. Modern scholars have generally shared this opinion; see, for example, H. Jacob Katzenstein's now-outdated The History of Tyre (2nd ed.; Beer Sheva: Ben-Gurion University of the Negev Press, 1997).
(2) Hanno's Periplus, a Greek translation (and possibly abridgment) of a Carthaginian report describing an expedition beyond the Pillars of Heracles in the sixth or fifth century B.C., is preserved in two Medieval manuscripts. You can find English translations in Al. N. Oikonomides' Hanno the Carthaginian: Periplus or Circumnavigation (of Africa) (Chicago: Ares, 1977) and Edward Lipiński's Itineraria Phoenicia (Leuven, Paris, Dudley: Peeters, 2004). For an analysis of the language in the Periplus, see Stanislav Segert, "Phoenician Background of Hanno's Periplus," Mélanges de l'Université Saint-Joseph 45 (1969): 502-518.
(3) While not "literary" per se, the Greek text of the treaty between Hannibal Barca and Philip V of Macedon in 216 (see Polybius 7.9) seems to have been translated from Punic. Elias Bickerman addressed this long ago in his article "An Oath of Hannibal," Transactions and Proceedings of the American Philological Association 75 (1944): 87-102. An excellent work on the subject is Michael L. Barré The God-list in the Treaty between Hannibal and Philip V of Macedon: A Study in Light of the Ancient Near Eastern Treaty Tradition (Baltimore and London: John Hopkins University Press, 1983).
If I find the time, I can also try to discuss some of the more interesting, "literary" inscriptions. I hope this answers your question in the meantime! :)