Yea they aren't sposed to be on their phones,but it's impossible enforce, at least where my kids go to school.
I would say we are at 80% success. Some teachers are just lax about it and that's probably always going to be that way. Some teachers are absolutely militant about it. Most are reasonable and enforce no phones when class is functioning. I for example allow phones once we are done as a class (last couple minutes or you finish your test or we take a couple minute break so I can transition to something else). The thing that's nice about the phone in school is the same reason many parents lean on it, it's easy classroom management. Let the kids use their phones and they are mostly all quiet and stay seated. It is creepy though to look out at a room of 30 teens and none of them are talking to each other, they all are just silently on their phones. So I've been trying to do more phoneless breaks, even giving them something to talk about or pairing them up and insisting they report back on some kind of non-academic related topic.
Do we have kids who just refuse sometimes? Yes. Luckily administration supports us and will call their parents, will tell the kids they can't return to class until they play ball, etc. If enforcement isn't working at school, I believe that it's because 1) teachers aren't trying 2) admin doesn't support the teachers in it 3) the parents won't back the administration. If all 3 are mostly on the same program, phone use can be significantly reduced.