Real talk, police can force you to unlock your phone if it’s locked with biometrics (fingerprint identification or facial recognition). The fifth amendment protects you against self incrimination, which includes providing the passcode to your phone.
If you have an iPhone, press the side button five times before handing it over to disable biometrics and require passcode for access.
The 9th Circuit ruled that it’s legal for an officer to unlock your phone by making you look at it or by pressing your thumb against it while in handcuffs. My comment is advice on how to prevent that from happening.