As I studied social psychology at univerity I am obviously aware of Stanley Milgram's work which demonstrated, as he said

"Ordinary people, simply doing their jobs, and without any particular hostility on their part, can become agents in a terrible destructive process.
Moreover, even when the destructive effects of their work become patently clear, and they are asked to carry out actions incompatible with fundamental standards of morality"

Not sure a rule about confiscating a banned mobile phone and that failure to honour the rule was met by a request to surrender it quite comes under something that is "incompatible with fundamental standards of morality"

What is sad is that the apparent escalation of something as simple as an understood rule for all pupils should result in a conflict between home and school that could result in the pupils exclusion.

As one head teacher has commented conflict with parents happens

'Schools have to manage thousands of cases ..., of bullying, allegations against teachers, refusals to attend detentions, claims of injustice and grievances, sometimes tactical, felt by children whose parents feel the best way to support their child is to attack their school.'

I'm sure the school would prefer to resolve this kind of situation without draconian measures but also cannot afford, if there is to be any discipline, to have a pupil deliberately flout a rule either.