Does the screen go to sleep while you're on the phone call? If you have the phone up to your ear the screen should go to sleep. There are a few reasons why this might fail. If your sensors are dirty, usually at the top of the phone near the camera, if it's dirty the phone doesn't see any difference from touching your face and not. Long hair over your ear can cause this also. Your sensor might not be working correctly, this a last ditch thing but easy enough to test. Call someone and put your finger over the sensor if the screen doesn't go dark there might be a problem. Of course if you're using an app that forces the screen on to conference call that is most likely the issue as your screen must sleep while up to your face to disable the on screen buttons.
Posted via the Android Central App