If the student had a notepad or copybook, in their bag and the teacher thought there was 'inappropriate material' in it and so asked the student to hand it over for examination, would we expect the teacher to wait for a parent to be present?? Ok, a phone is not a copybook, but they are both the student's private property, and the fact they have brought it onto the school premises surely imposes responsibility not to use it inappropriately and also imposes responsibility on the school to ensure it is not used for any inappropriate purpose. BAck when I was in school it would more likely to have been a student pulled up over having a 'magazine' in their bag - would anyone have complained if teacher ordered someone then to empty their bag to show what was inside??
So yes, students have rights to privacy, but when they breach their own responsibility towards others, then I think the school has a right to take action. Obviously as long as they do not forcibly take the phone from the child. As for calling in the parent, would this not have just given the child opportunity to delete the material, or else wasted hours of everyone's time keeping the child under supervision until the parent got there. On balance, I agree with the taechers approach.