See an ophthalmologist. I've used my phone for hours and not suffered any pain. If's not the phone, but it could be the color temperature of the phone that's affecting something in your eyes. (A lot of screens have a lot of blue output, and that bothers some people.) You might benefit from a slight yellow plastic screen protector. (But get your eyes checked first - bring your phone with you. This isn't a medical forum, so don't take chances with your eyes here - see a professional.)