u.s. customs can just make you unlock your phone and search it without a warrant for no fucking reason.
they did it to me once at the airport.
i got pulled aside where i was questioned by a hispanic bitch while they unreasonably searched and seized my phone and looked through my gallery and private messages without any probable cause.
then when they saw i had nothing illegal she kept interrogating me about the irrelevant private information they just uncovered instead of just letting me go right away.
next time you travel abroad make sure to wipe your phone, or some dumbass female agents with the authority to violate your constitutional rights might put you through this brutal humiliation ritual.