Would this be a federal ban, a state-level ban managed by education boards, or something else?

And how is it enforced exactly? Are parents held responsible, or are state education funds impacted somehow based on smartphone use?

Would we need a federal mandate to require flip phone / feature phone support? The last time I tried to find a feature phone it wasn't easy, many depend on 2G/3G networks which are losing support and carriers have absolutely no incentive to carry feature phones when smartphones are all that sell.