I know of a mainstream girl school where the girls must deposit their phones in plastic containers in the front office at the beginning of the day and take them back at the end of the day.
In one boy’s yeshiva high school that I am aware of, there is a rule that cell phones must be turned off during learning. If they forget to turn them off, they are definitely not allowed to answer. If they answer, the phone is confiscated and not returned.
Cell phones are a problem for many reasons. If a yeshiva has a “no cell phone” policy, they must enforce it, with seichel.