For exactly the border search scenario, I wish smartphones could be imaged and restored as easily as PCs. Imagine booting the phone from a flash drive, making an encrypted image of the phone on said drive, and writing a fresh OS before reaching the border.
There's no deception required to protect sensitive data or avoid the seizure of an expensive phone. Consent to unlocking the phone, refuse to unlock the drive. The drive gets seized and you go on your way (if you're a US citizen entering the USA).
Some time ago, Android with a custom recovery could come close to that, but it was fussy and as far as I know, no longer viable. Increased use of TPMs for storing credentials seems to be at least one of the reasons.
There's no deception required to protect sensitive data or avoid the seizure of an expensive phone. Consent to unlocking the phone, refuse to unlock the drive. The drive gets seized and you go on your way (if you're a US citizen entering the USA).
Some time ago, Android with a custom recovery could come close to that, but it was fussy and as far as I know, no longer viable. Increased use of TPMs for storing credentials seems to be at least one of the reasons.