Can you please post photos of the actual coin? I'm not an expert on ancient Greek coins however as far as I can tell coins of Philippos II and Alexander the Great are among the most commonly counterfeited ones. Good news is it is possible to buy the most common ancient Greek coins for 15$ so price alone doesn't mean it's counterfeit. I don't know if this coin is common or not.
EDIT: I misunderstood the post and thought you're asking about the coins authenticity when in fact you're looking for info about the coin. I can't help with, all I know is that Philippos II was the father of Alexander the Great. You can find a bit more info about his coinage on WildWinds but not much more:
http://www.wildwinds.com/coins/greece/macedonia/kings/philip_II/t.html
I collect and deal in ancient Roman coin. In case you're looking for affordable ancient coins or need any help with the coins you already have send me a message.