One advantage of being a US citizen. If I'm entering the country and they want to see my phone, I can tell them to get lost. Worst they can do to me is hold me briefly and confiscate my phone for a while. That would be annoying and costly but not a particularly big deal.
I can't do that when entering any other country, of course, but they seem to be much less likely to try it.
You might want to consider whether your definition and the government's definition of "briefly" agrees.
For example Carlos Rios, a naturalized U.S. citizen was held for a week before being released. Peter Sean Brown, another U.S. citizen born in Philadelphia was detained for three weeks. Source: https://www.propublica.org/article/more-americans-will-be-ca...
So far they are, for citizens. The worst case I've heard of was a citizen who was held by ICE for a few hours because they didn't believe him. Which, don't get me wrong, is bad given the racist underpinnings of it, but not something that worries me in and of itself. And yeah, they've gone so far as to deport US citizens from time to time over the years, but it's not anything like systematic.
They're not refusing entry or holding citizens indefinitely for refusing to unlock their phones at the border. Maybe they will, but until it starts, what I said holds.
When I say “they”, I’m referring to the people ICE reports to. Precedent and rules don’t constrain them, so what happened in past years seems irrelevant.
I can't do that when entering any other country, of course, but they seem to be much less likely to try it.