I experienced this issue when I replaced the frame on my phone and had to transfer everything over. The proximity sensor wasn't close enough to the glass onto the new screen so I placed a folded piece of paper between the sensor and the black piece that screws down. Make sure you place the rubber piece in the frame before installing the proximity sensor. I installed a program called sensor kinetics to see if the proximity sensor was working properly. I hope this helps! It took me a couple hours of troubleshooting to come up with a solution. The issue is that the proximity sensor wasn't close enough to the screen and I believe it was reflecting off the glass and getting a false reading. Download that program and scroll down to the proximity sensor. It will either read 5CM or 0CM. Mine was always reading 0CM. Something else to note: if you unplug the sensor with the phone on, you will need to reboot the phone to get a reading in the program.