What about the less convoluted scheme of "I forgot it?"
The "I do not recall" answer in high profile trials is so common that it's essentially become a meme. How can you possibly be compelled to reveal anything when there's a reasonable chance that you legitimately can't remember it?
I suspect you’d actually be ordered to provide access to this device (which you regularly access).
In particular, I don’t remember the pin or password to some devices and accounts. They are shapes, on the pin-pad or keyboard. There are enough alternative ways of logging in (the apple face thingy, yubikey, you could hypothetically have devices setting up arbitrarily complex interlocking login processes) that I suspect the court would just define what they want, rather than how they want you to do it.
I could be wrong though, no actual experience here with the legal system at all.
My guess is you would be charged with obstruction of justice. This would be similar to you destroying evidence requested under subpoena. Now, as a matter of legal strategy, this may be a better charge to face than whatever is on your phone. Of course, this is not legal advice and YMMV.
That's fine, until a piece of supporting evidence (photo, email, faceID hash or whatever) establishes that you interact with the device on a regular basis.
The "I do not recall" answer in high profile trials is so common that it's essentially become a meme. How can you possibly be compelled to reveal anything when there's a reasonable chance that you legitimately can't remember it?