I'm thinking of walking pass and unplugging his phone.
Why are you planning to unplug his phone?
Because he doesn't need a phone to live.
This is only going to make him upset. You are better off asking him to put his phone away or explaining to him why you want his phone to be put away.
I'm going to do it, what's the big deal?
The phone is their property and not yours. Taking someone else's phone will probably only make them agitated.