cannot take responsibility for such expensive items in such a busy environment
then they can have no reason to ask for the information.
If they have no responsibility then the responsibility lies elsewhere the information belongs there.
If the phone was lost then the school could do nothing about it as they are not the account holder.
As a school governor I would be worried about retaining this information given the implications of loss or inappropriate access and use. Imagine if someone got hold of the information that would give them access to all of mobile numbers for the children in a school.