Its definitely not a philips screw head, you just need to look at it to see that. Its a five pointed shape which is a TORX, which is used by apple in nearly everything they make. Size would be a 5 or a 6 I would guess as I haven't got my TORXs at hand.
A philips screwdriver wouldn't work, you could try a flat headed precision screwdriver if you couldn't be bothered to get the correct one, however you might find it hard to get the right size.