[foob]

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?

[bee_rider]

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.

[takinola]

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.

[omginternets]

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.

[fluidcruft]

Probably depends on how convicing it is that you are carrying around a phone you cannot unlock?