To be completely accurate the Constitution doesn't apply anywhere within 100 miles of a U.S. border, which includes airports. This covers something like 60% of the population of the United States.

https://www.thenation.com/article/66-percent-americans-now-l...

https://www.aclu.org/other/constitution-100-mile-border-zone

Just a nitpick, but the Constitution still applies (and worldwide between US GOvt and US Persons), but the courts have decided its rules against unreasonable search and seizure don't apply for customs and immigration purposes with certain distances of a port of entry.

Plenty of laws apply. They thing to remember is that you can't give up something you don't have. Use a blank dumb phone when crossing, restore afterwards.

The entry requirements aren't just "show me the phone you have", they include "give me your social media details".

Turning up with a burnder phone is a guarantee that you're going to spend hours in an immigration office.

I've not heard of demands for fb/twitter/email passwords. More of a concern for non-citizens -- don't post anything publicly I'm afraid.