What happens if you use the postal service to deliver your phone across a border? Are the same authorities who claim the right to search your phone if it is on your person at the border also claiming the authority to confiscate and duplicate your phone if it shipped/mailed? Do you have to put your password on a sticky note on the the front of the phone? And if you ship the physical device but transfer the data separately does that change the expectations?
It is interesting that condensing information into a digital format that can be easily duplicated and searched (before or after duplication) seems to change the expectations for the authorities and I think for individuals.
I think this is another example of the modern digital world/economy has left the legal system in the dust.
Physical objects usually don't reveal this much at once and require a warrant. With a border phone search, there's no due process at all. If you're so afraid of bad actors that you're willing to subject yourself to this, you're free, but the bad actors have won.