I would pay a good premium for an iPhone with a distress code that unlocks the phone into an environment with some fake but plausible contents. Bonus points if it optionally wipes the real user partition upon entering the code.
You can also say "Hey Siri, whose phone is this?" and your phone will lock down the same way as described above.
Of course, this doesn't protect from the $5 wrench attack, but plausible deniability only goes so far as well in a targeted attack. At least, depending on your local laws, law enforcement may not be able to compel you to provide your passphrase, but they can easily force you to use your biometric data, so this protects against that.