I would agree with you if we’re talking about something like the ability to search a car, where the cop is not allowed to without the owner’s permission (assuming no probable cause or warrant). In that case the cop usually figures out a loophole to manufacture probable cause or manipulate the owner into agreeing to a search. And then there’s nothing a lawyer or judge can do later, because it’s the cop’s word vs yours.

But if we’re talking about a law that actually says the cop cannot take your phone no matter what, and they do, then any public defender would be able to point it out and the judge would certainly have to enforce it. I can’t think of a way the cop would abuse their power because, in this case they don’t have it.

I could be convinced based on the actual wording of the law, though.