Offsetting part of the punishment to the parents (having to get them to come in to the school to collect the phone) is going to help get the policy reinforced from home in most cases.

My kid’s school had a similar policy. I didn't mind having to go out of my way to collect the phone and didn’t pass any of that on to my kid, they were annoyed enough about having it confiscated that it only took a few times before they modified their behaviour accordingly.