Is this legal?

Is it legal for a school to hold private property like this?

“If a cell phone is confiscated by an administrator or teacher, parents will be required to pick up the phone. If this occurs a second time, the phone will not be returned to the student until the end of the semester.”

I’m also pretty certain this “rule” is not in writing, but only recently instated. Yes, cell phones are supposed to be out of sight during school hours, but none of the above is listed in any rules or guidelines.

So is it illegal for the school to take someones cell phone like this? I’d think it’s stealing, they’re not the police. Why does everyone think just because you’re in a school means you lose constitutional rights?