The legalese is thick but this is a notable point I saw from a quick skim:
5.3.2 "Passcodes or other means of access may not be utilized to access information that is only stored remotely."
looks like they can request your passcode to unlock the phone so anything local and/or cached before they disable network connectivity would be there.
That's not notable at all given a lot of content is synced to the device, not even counting temporary and cache files.
They will be disruptive to your life if you, as a U.S. citizen, refuse to unlock your phone on the U.S. border. But it is my understanding they cannot constitutionally mandate you provide a passcode to unlock your phone. But they may confiscate your phone from you.