I’ll never bring my phone on an international flight again. Neither should you.
Quincy Larson

If “The border is technically outside of US jurisdiction, in a sort of legal no-man’s-land.” — who are those people? They have no rights outside US jurisdiction, because they are nobody outside US. So technically you have your rights, you just have no power to enforce them. But you lose so many rights to fly plane, phone privacy is not special.