black screen on phone call
Sounds like the screen timed out or the proximity sensor is blocked maybe by a case or screen protector. If thats not the issue An app can keep screen on during calls or just increase the timeout duration in Settings---->Display to 5-10 minutes yourself.
https://play.google.com/store/apps/details?id=com.vorlan.screenoncall.free
*** ~~ßocephous™***