Wheelwell moulding screws Clean out the Phillips heads. Get a sharp awl or ice pick and dig out all the corrosion down in that little "x" so the Phillips bit can get a grip. It's surprising how much difference this will make. Then line the screwdriver up and give it a couple of cracks with a big hammer. All of this along with PB Blaster, brake fluid (if you don't care about paint), oyster slime, elephant sn*t, or your favorite other penetrating lubricant.
I always use a 1/4" drive ratchet, 1/4" socket, and a hex drive Phillips bit in the socket. That way you can get a lot of force behind the ratchet head to hold the Phillips bit snugly in the screw head.
rust trim screws Rick, A old body man showed me a trick many years ago on these screws. Take a small, sharp chisel an give it a wack in the "unscrew" direction. then a phillips just unscrews it like magic. I have done all these other ways with good luck too, just use the chisel on the really tuff ones. Hope this helps, Mike