I also had an internal screw that was stripped on an iphone 4. Tried several different things but the one that finally worked for me was using a large rubber band. For those who haven't seen this trick, all you do is take a large rubber band and lay over the screw. It will fill in the negative space where it is stripped. Use the normal phillips heads screw driver and turn it very slow. It worked for me. I had tried for a couple of hours before this and was already very frustrated and had no faith. Am very thankful that it worked. I have no replacement screw and haven't put phone back together yet. Am hoping for as much luck in that it works without a replacement. At least this will help you get the screw out . Good luck