> This is why I think it's great when schools ban phones in class.

Agreed on the classroom angle, there are many reasons (e.g. cheating, concentration) to treat the availability of devices in a uniform way there.

> If you believe that smart phones are disastrous for kids

A focus on the handheld device also makes it easier to handle other related concerns that can't really be solved any other way, like "no social-media after bedtime."