It's pretty great; even my daughter agrees it's a good thing.
Kids now obvs do all have phones, but (in my daughter's public school in SF) they absolutely cannot use them during school hours at all, or they are confiscated.
Parents are clearly told "if you *must* contact your kid, ring the school office and ask them to pass on a note" - this obviously sounds archaic but in practice almost nothing is "that important" so kids do indeed get to go about their school day from start to finish without touching their phones.
Once the final bell rings, sure, all the phones come out, for all the usual purposes from social media to txt'ing parents arranging pickup, but the school day is sacrosanct. It works really well.