Tell us about yourself!
the method i used back in the day was to put the edge of a flat screwdriver to side of the screw and using the screwdriver like a chisel hamer the screw sideways and if possible back again. my first few bikes had phillips screws holding the cases together and they were always locked and this method worked 90+ % of the time. that side of the head impact just seemed to break whatever was sticky. Im glad they came to their senses and stopped using phillips screws.
also a lot of people don't know that the phillips screw was invented SO THAT the screw driver WOULD slip out of the screw. something about it being easier in manufacturing and assembly. I can't quote the source. i don't recall. but its an eye opener.