When on a call, the screen turns off; when I turn it back on to unmute I am not on the call screen and have to go back to it
Putting your phone in your pocket triggers the proximity monitor. When the front of your phone gets close to an object during a phone call, the screen automatically shuts off to prevent accidental touch inputs from the phone being against your face. However, the phone is not actually off! When you take it out of your pocket and thus away from the nearby object (your leg) which it assumes is your face, the screen will turn back on automatically, without you having to press the power button. When the phone re-awakens after moving away from the nearby object, it will show you the last screen you were on: generally, and in your case, it will automatically open up the phone control screen where you can quickly unmute your microphone. 

Here's what you're doing wrong

You're pressing the power button. This closes the phone screen and takes you back to your home screen. How you can fix your issue: Just don't press the power button before you put the phone into your pocket, and it still will automatically shut off the screen, and don't press the power button when you take the phone out of your pocket; it will automatically come right back on to your phone call control screen, where you can unmute the call very quickly.



Don't push the power button when you put your phone into your pocket, and don't push it when you take your phone back out.