How to lock the screen during a call?

[kuhinja]

When I call, my proximity sensor turns the screen off when I bring the phone to my face but the touchscreen remains functional so if I touch the screen with my face it wakes up and starts to open stuff during the call.

I'm looking for an option or app to lock and keep the screen locked during the call.

 

[Rukbat]

The default in a working phone is to lock the screen when it turns it off by proximity sensor. It sounds as if your phone is defective.