The key thing is that teachers can ban phones in their individual classrooms if the school permits it.

There are many schools in which the senior admin don’t institute phone bans (you’d be surprised how common this is).

Legislating it helps maintain consistency and parity between schools nation wide, which is important as it’s a quality of education issue, so the policy should be consistent across all schools.

I’m not from North America, but the situation is similar across most western democracies.