my iphone

I would first try to do a reset to see if it was simply and issue with the software. To do this you hold the power button and home screen at the same time until the apple logo appears. I just realized this process may be different on the newer iphone models. If the issue is still happening after the reset, then I could be a hardware issue and you may need to contact apple or get help from an apple store.

Did you have the display replaced?

Take the device to an Apple authorized repair location and pay for the repair.