Hello Rob,

It does sound like an issue with the digitizer/screen, if you have been inside the phone in the past it is entirely possible that you did not clean off all of the original adhesives and your screen is not sitting flush. You could opt to get a replacement digitizer/screen however the phone is 6 years old and you may very well be better off upgrading to something newer.

Visit swappa.com for deals on gently used phones.