I worked within an international terminal (KORD) and have taken hundreds of people through customs. I can safely say there has never been an instance where digital media is accessed, even in secondary which you're brought to for further assessment when under suspicion. Only thing I've seen is accessing recent calls for passengers suspected of lying on their visa and being in contact with relatives; but if their phone is locked they can't do jack.

Without rambling too much, unless you're like actively commiting some type of criminal import activity, no border agent will care what you have.