The physical seizure is a huge problem. If seizing a cellphone by simple diktat is allowable, then name me any personal property that can not be similarly seized. Money? Sure, why not -- might be drug profits, after all. Car keys? Sure, why not -- might have drugs or (gasp!) guns stashed somewhere within the vehicle.
New Jersey v. TLO is/was a different kettle of fish entirely, and a poor citation for your argument against a student's property rights. When a person is seen smoking, and smoking is prohibited by rule in a given area, it is completely reasonable to postulate that said person has more cigarettes either on his person or otherwise readily available, as for instance in a purse. In any case, the purse was searched, not seized except during the search; only the then-discovered contraband was seized.
In the case of a cellphone, no such precursor action as illicit smoking exists, and there are therefore no grounds whatever for any seizure of any duration.
The law says otherwise.
Schoolchildren have legitimate expectations of privacy. They may find it necessary to carry with them a variety of legitimate, noncontraband items, and there is no reason to conclude that they have necessarily waived all rights to privacy in such items by bringing them onto school grounds. But striking the balance between schoolchildren's legitimate expectations of privacy and the school's equally legitimate need to maintain an environment in which learning can take place requires some easing of the restrictions to which searches by public authorities are ordinarily subject. Thus, school officials need not obtain a warrant before searching a student who is under their authority. Moreover, school officials need not be held subject to the requirement that searches be based on probable cause to believe that the subject of the search has violated or is violating the law. Rather, the legality of a search of a student should depend simply on the reasonableness, under all the circumstances, of the search. Determining the reasonableness of any search involves a determination of whether the search was justified at its inception and whether, as conducted, it was reasonably related in scope to the circumstances that justified the interference in the first place. Under ordinary circumstances the search of a student by a school official will be justified at its inception where there are reasonable grounds for suspecting that the search will turn up evidence that the student has violated or is violating either the law or the rules of the school. And such a search will be permissible in its scope when the measures adopted are reasonably related to the objectives of the search and not excessively intrusive in light of the student's age and sex and the nature of the infraction.
If seizing a cellphone by simple diktat is allowable, then name me any personal property that can not be similarly seized.
That is not the standard in play - it is perilously close to a simple strawman argument. You keep going on about property "seizure", when that's not even remotely the issue - the only property being "seized" is that done pursuant to a search. No search = no seizure. Additionally, there must be a "reasonable suspicion" that searches will reveal evidence that the law or the rules of the school are being violated. At no point is the school asserting that cellphones are not the property of the student, nor are they claiming carte blanche to simply steal cellphones. Instead, they reserve the right to search cellphones in accordance with reasonable suspicions that infractions are or have occurred. Simply taking a student's car keys - or his cell phone - for no reason other than that they claim they can does not in and of itself reveal evidence of infractions, and hence it is not permissible, in and of itself. But, since that's not what they're doing, it's not a problem.
In the case of a cellphone, no such precursor action as illicit smoking exists...
That is not for you to determine - the reasonableness of searching am individual student's particular cell phone is based on the totality of the circumstances in that unique situation, per TLO. To make a blanket assertion that such a search is never justified, in addition to being a misunderstanding of the law, is simply silly.