He should have backed up the phone before travelling then wiped the phone to an innocuous state before getting on the plane.

Want to see a really confused border agent? Travel without a phone. Fedex your phone to your hotel/home. Read a book on the plane. The concept that someone doesn't have a phone/computer drives cops insane.

One of the wikileaks crew pulled this one in NY. Several agencies were a set to grab his devices and detain him until he unlocked them ... But all he had in his carry-on was a magazine. His devices had been wiped and sent by mail. He re-imaged them only once he was home and safe. No devices to unlock, no reason to detain him.