In addition to the good advice above:

https://apps.apple.com/us/app/mobile-justice/id979642692
https://play.google.com/store/apps/details?id=org.aclu.mobile.justice.ca&gl=US
No doubt, your phone is always with you.

Whether at a protest, a polling place or on the go, the ACLU's free Mobile Justice smartphone application allows users to:

RECORD encounters with public officials and law enforcement while streaming to your closest contacts and your local ACLU;
REPORT any abuse by authorities to the ACLU and its networks; and
EMPOWER yourself with up-to-date information regarding your rights as well as important actions and happenings in your area.

I got it just for the STFU advice.

You may also want to know your rights against search. (see below)

At the very least, learn to lock an iphone quickly by pressing and holding the power button and volume button(s), which are opposite each other. Whether or not you shut down or use the emergency function, a password login is required.

This is the "below" part:
A warrant is required to search your phone, like your home and home contents.
https://www.eff.org/issues/know-your-rights
A 2014 Supreme Court ruling. Remember to GOTV if you want any rights at all!!
https://www.democraticunderground.com/100216821536

but the issue of forced decryption ( "look at the phone, use your fingerprints, hand over your password" ) is still "out there" even if every ruling I have heard of has gone against forced decryption (IANAL!)
https://www.nolo.com/legal-encyclopedia/if-the-police-arrest-me-can-search-cell-phone.html

IN ANY EVENT, I recommend a very long password, even if you use biometric ID, because upon restart, it is required, and (this is important) most phone-cracking tools take exponentially longer to crack the contents of the phone if it is seized with every extra letter or number in your password.

Again, IANAL, but a password is generally considered "intellectual property" subject to more protection than biometric ID. And, it's harder to coerce, especially if your phone is not shut down, requiring a password login, if you are unconscious.

Unscrupulous cops? Don't bet your future on it.

Cops have cellphone cracking gear.

I do believe that much of the cellphone evidence collected in the Jan 6 coup attempt has been obtained from recipients of messages, who saved or screen-shot the messages before they were "deleted".

For any more detail, visit EFF's site. https://eff.org -- Electronic Frontier Foundation
I did not reference any law firm's website, though they may provide more detail.