As facts are presented, the daughter is completely in the wrong. I would demand character witnesses if I were the daughter's lawyers and actually had a chance at winning this case. AKA, I would get real life people to give testimony in court as to whether the girlfriend was a terrible person or not. If they could find multiple people who could testify to this, then you know the case is more complicated than at first glance.
But that is clearly not the case. The adult figure was taking away a PRIVILEGE as a consequence for intolerable actions. There was in no way any physical discipline at all, which is controversial as all hell. And sorry CG, but you can't argue that the girl didn't know what she did to have her phone taken away. She knew what she did wrong, and the father took away her phone. There is no misunderstanding or miscommunication here... just some girl who felt entitled and a mother who was only too happy to take the side of her child, right or wrong.