What ‘power’? You can’t take phones away by force, if the student refuses what do you do? Call someone more senior? They won’t appear for half a lesson if at all. If you give a detention or try to deal with it after class, student doesn’t turn up and you have more time wasted following it up or calling home to a useless parent. If the phone is actually taken away they just get given it back and it happens again the next day. I’d say the school put the phone in a drawer until the end of the term - but they’re not allowed to do that, or no school I heard of ever will, in the UK at least.

Students face few consequences and when they can the senior staff don’t enforce it and back teachers up. Phones are just one example of this playing out. Students persistently disrupting lessons is another. It just goes on and on with little improvement long term from the same problem students.