You don't get that option. The
first thing that happens to everybody
who is attempting to enter the US and
flagged is that they give you a form
to write down all keys and passwords
you might have, they will then unlock
your phone and attempt to find anything...
You see, even if I'm forced to write down a password, if that password decrypts a 3TB file filled with shit data that LOOKS like it's still encrypted somehow, and then throws errors on further attempts to decrypt, the goal is achieved.
I have old laptops I'm ready to throw in the garbage. I have old, dying hard drives I can partition with nonsense. If that's all I'm carrying, then border patrol can merrily spin their wheels on it, and it will never contain anything valuable, despite appearances, because it is junk and contains junk by design.
For phones? Well, if all I'm carrying is a 1990's candybar phone with a 4 digit pin, and I "unlock" it for someone, and it shows "NO SERVICE" because I never paid money to activate service on that phone, even though it's the only phone I'm carrying, the goal is achieved.
If I'm carrying a trashy 2008 edition smartphone, and I unlock the bootloader, and reflash with a custom ROM that contains 500 garbage contacts with (555) 555-5555 numbers and John Doe as the name, and then encrypt an SD card with a FAT partition that contains a single 4BG encrypted file that's really just random data, or maybe 9000 files with misleading file names, but all contain junk when decrypted, the goal is achieved.
If I jail break an old iPhone C that I bought refurbished, second-hand for $50 and then I activate it's password protection as the number 1234, but never place a SIM card in the slot, and load it with thounsands of random images from the internet, and tons of fake notes that look like Base64 data, and that's the only phone I'm carrying, the goal is achieved.
Your tangent about drugs is an unrelated digression.
Staging junk devices with garbage data, for the purpose of sacrifice to security theater, is fun, easy, and anyone can do it if they've got the next week or two to pack their bags.