

BFU and AFU doesn’t matter if the authorites don’t obey laws.
You can refuse all you want, they’ll just jail you for refusing.
The UK already jail people for refusing to unlock their devices. Now with a president of the US who does not respect the rule of law, the same, or worse, will happen.
Just don’t have anything political on your phone, let them search all they want, there’s nothing there.
Keep any such materials on a Non-US cloud account, in encrypted format, without any personally identifiable information on that account. Hopefully you access them through VPN/Tor to make it difficult for them to determine the existence of such accounts.
Don’t have anything political or religious stuff on your phone.
Encrypt and upload those stuff to a Non-US cloud account, then delete them all from your phone. If you want to be extra safe, after you upload all the sensitive materials to a cloud account, make a separate back up of you non-sensitive data, then wipe your phone and then restore. Any traces of sensitive political stuff should be gone, since modern phones would delete the encryption key tied to the old data. Make it look as “normal” as possible. Keep your photos on their, pets, family photos, everything you’re fine with the government seeing (so, nothing political).
And make sure you have your documents, take photos of all of them and back up to cloud. If you were born outisde of the US, the burdon of proof of Citizenship apparantly lies on the claimant. Even if you were born in the US, still have documents ready.
If its non-essential travel, like tourism, I’d suggest just not cross the US border (neither in or out) until times are safer. I’d only consider exiting the US border if you are planning leaving permanently, otherwise, just don’t cross the border.
There are plenty of places within the country that you can visit without getting caught uo with the border shenanigans. (But please do not travel to a republican jurisdiction)
So, this is work travel? Oof, good luck. Have your documents ready and you should be fine.
Act nice, Don’t argue with the border agents, you can’t win a confrontaton with them. If anything goes wrong, your only chance to win is in court (and hopefully, the rule of law hasn’t completely collapsed)
TLDR: Just delete all sensitive data and you can go ahead and consent to searches without worrying, they won’t be finding anything.