Very often when I'm talking on the phone, the screen turns on and my chin and ear presses all the buttons. Often this starts facetime, turn off the sound, and is just very annoying. Is there any way to make the screen always be off when I'm talking? I'm using a regular iPhone 6.
Sounds to me like a bad ambient light sensor and/or the proximity sensor. Both are a part of the front facing camera assembly, and you cannot buy them separately.
It should be covered under warranty, but if it's a result of a drop or water damage, then it's not covered under the standard warranty and you may have to have it repaired, either by yourself or a pro.
If you feel comfortable with the repair, here are some tips:
- When removing the digitizer assembly (touchscreen) with a suction cup, take extra care to avoid severing the digitizer and LCD cables.
- If you damage the home button or its cable, then TouchID will no longer work.
- Here's the guide
Of course, you could always take it to a pro, just be prepared to pay likely $100+, unfortunately. Maybe even $150+, depending on where you go.
If it's not under warranty, though, wait until the iPhone 6S comes out in less than a couple of weeks, as once the iPhone 6 is no longer the newest, parts and repair costs should be lower.
If you don't want to get the sensors repaired or change how you hold the phone, simply lock the phone once you have accepted the call.
Now the large problem of face touches is mitigated by the lock screen.
Some people either have large ear cavities or don't hold the phone stable or close enough for the sensors to know it is by your face. This locking works and you don't need to use earbuds or other remotes to avoid premature hang up, adding a contact, dialing sounds, etc...
I was having a similar problem. It appears to be fixed, oddly, after I opened the camera app and used the front facing camera in the dark making the flash work on manual and then auto. I'm not sure if it was not talking to the camera or what the problem was but sometimes its the easiest things that fix it.
To check the proximity sensor, you can use Device Doctor (https://itunes.apple.com/vn/app/device-doctor/id1178246735?mt=8). Beside proximity you can check the other functions as well. Good luck
another cheap and easy partial fix (at least for the FaceTime part when away from home) is to go into Settings > Cellular and turn off Cellular for FaceTime (in the list of apps at the bottom). My wife has this problem and 99% of the time it's FaceTime that her cheek hits and it's always away from home/wifi.