If I understand current law, one cannot be forced to supply a password or passcode because of 5th Amendment rights against forced, potentially self-incriminatory speech.
A fingerprint is regarded differently. You can be forced to supply a fingerprint because it is something you are, not something you know, the latter being speech which cannot be compelled.
One could use biometrics like facial recognition and still enjoy 5th Amendment protections if a sequence of facial gestures were required to unlock a phone. While the biometric features comprising the sequence are indeed something you are, the sequence is something you know, and constitutes speech, which you cannot be compelled to supply.
So yeah, Officer - I'll stare at my iPhone for as long as you like. It won't unlock until I blink my right eye twice within 1 second and raise my left eyebrow immediately thereafter.
edit to add missing word
Though practically, I doubt many people will want to scrunch their face each time.
I actually thought I did at first, and was a bit annoyed. But it turned out I was just holding the phone far too close to my face when I didn’t have glasses on.