It's definitely a mix of the actual phone pouches and the bans giving teachers actual authority and permission to confiscate phones when they're out and disruptive. IMO there's likely a shift that happens with pouches where there are enough kids following the rules and only having one phone in the pouch that it tips the social balance over. That would be harder with just teacher enforced bans I think.

It's definitely a hard problem over all balancing their completely disruptive nature if there's no bounds to the issues around safety and parental worry from not being able to contact their kid all the time which phones have made the norm.