You are NOT going to find an actual law that covers this.....like you state you signed a contract with the school when your parents signed you into THAT school. basically the rule of thumb is [I taught at a senior school before moving to the USA] and it was stated that no phones where allowed in school.......NOW this was allowed to slide if I did not see it, did not hear it, you did NOT have your grubby paws on it when I am teaching, if you DID then I would remove it from you.........if it rang while I was teaching I would suggest that everyone took a moment to ensure their phones where turned OFF or I would remove every-ones phone etc etc.................but have also took the blame for it being MY phone that went off when some ones bag was near to mine, so that child did not get in any more trouble than they already where.........
The way around the whole holding it in a safe thing is your parents pop along to the school and ask for it back period, they will NOT refuse your parent the 1st time, if it is a habitual thing then you remaining in the school can be put in jeopardy..............so walk with it on to school enter school gates TURN IT OFF and this will become a non issue.

