While the general approach of our group involves close attention to a text - as we have found that reading aloud and re-reading does wonders for our awareness of the language, density, and astonishingly complex beauty of certain works - there's never harm in enriching one's sense of the tale and tradition, the mythos from which a great work is fashioned.
Of course the Philoctetes has received far less critical scrutiny than, say, the Oedipus plays of Sophocles, but this is not to say it's been ignored. In fact a good deal of ancillary material along with the text and some interpretive observations, artwork, and more has been gathered together - lovingly, if one can judge, by Oscar Mandel.
Prof. Mandel's book, entitled Philoctetes and the fall of Troy (Lincoln, NE: University of Nebraska Press, 1981) is a valuable study of virtually every reference to the central figure of Sophocles' tragedy.
But the best part is, it can be downloaded as a .pdf file here. Mandel quotes liberally from ancient commentators as well as from fragments of the actual works of Aeschylus and Euripides, showing how Sophocles reworked the tale in his own unique way. He also traces the iconography of the character through the Renaissance into the 19th century quite thoroughly.
The generosity of sharing such a trove of scholarship is remarkable and deeply appreciated.