this has not happened to me yet, but as a non-US citizen with a green card, if USBP told me "give us the code or you're not admitted" the next time i try to enter US, i'm gonna give them the code
Still, give them the code if you want.
It's pretty unbelievable that you have reduced constitutional rights as a citizen re-entering the country.
There is inconvenience of being deported but frankly risk of giving access to all clouds account to random official is just too high.
There is also risk of them putting you in jail but I am not sure if unblocking phone really mitigate it.