The cell phone policy can be enforced without destroying the student’s privacy. Requiring anyone to empty pockets in front of others is a tactic of public humiliation.
Even in airport screenings which involves matters of life and death, you can ask for a private inspection. If a school needs to do inspections, then they can bring in an outsider who is not part of the community to do the inspection privately and only report to the administration whether the suspected item was found or not.