The issue is kids aren’t making phone calls in class. They’re on social media. They’re listening to music. It’s usually not obvious and disruptive to others, but still impacting their ability to focus and learn. Banning them outright causes kids to be sneaky and resentful, but allowing them can be detrimental, especially with the impacts on mental health. If you collect them before class (I’ve seen teachers use shoe holders hanging on the door) kids will bring in an old phone and turn in that. If you use the locked bags, same deal. If you scramble the service so they phones are unusable then you can run into issues in a real emergency.