If we ban phones in schools then the problems we have with phones in schools* will disappear because there will be no more phones in schools.
Banning phones won’t solve all behaviour issues. Nobody claims it will. It will, however, stop problems with phones. Because there won’t be any.
*Getting them out in lessons, taking photos of each other, a certain degree of cyberbullying, phoning home to wind up mum or dad about a small issue before we’ve had a chance to sort a situation and phone home ourselves, etc.