There is no one authority that can enforce a "global ban" anyway.

I believe this is just an appeal to school authorities worldwide - asking them to recognize the downsides and take concrete measures in their own way to keep smartphones away from learners in the classroom setting.

If enough school boards agree and take such a stand -- others are likely to emulate / follow, parents and kids will come to accept it and adapt, and it becomes a defacto global ban.

I guess, somewhat similar to how public smoking has now become near universally "banned" or at least shunned.