I need to contact them in case of an emergency doesn’t mean the phone is out. Also the only emergency that matters is if the kid is in danger and needs to call someone. If Dad falls down a flight of stairs and breaks his neck you either A, go pick the kid up from school or B tell him when he gets out of school. The kid isn’t a paramedic.
Also kids don’t have rights at school. That’s why they have the ability to search all their lockers, backpacks, and vehicles without a warrant.
There is no law that says you have a right to have your phone in your hand, or it would be illegal to seperate us from them to go through metal detectors and such at airports, courts, etc