Right, and grandparent has a typo. True you are not required to hand over the password, but they aren't required to give you back your phone if you don't.
> There is no limit on how long the devices can be held but the agency said the policy was to keep devices for no longer than 14 days unless it took longer to examine them.
Right. So they don't give you back your phone. You may get it a couple of weeks later. Very convenient for your trip.
... and they're doing it for purely punitive reasons. We all know they're not "examining" the phones in any meaningful way. It's too expensive and failure-prone.