[Android Central Question]

When I am talking on the phone my phone does not blackout so my cheek hit things that opens stuff

[Mooncatt]

The phone should do this automatically when the proximity sensor detects your face during a call. It can be hard to see, but it's usually near the front camera. If this is malfunctioning, then the phone wouldn't know when you're holding the phone to your face and would stay on.

Have you tried pressing the power button to turn off the screen as a workaround?

[B. Diddy]

Welcome to Android Central! Which phone do you have? Some cheaper phones actually don't have a proximity sensor. These phones rely on a kind of lockscreen that appears when you're on a call, requiring you to double-tap or swipe up to get back to the dialer.