Are they pulling over passing Bentleys the peruse the phones of those inside? If one of these cops sees another cop passing, do they check their phone? Do they go into the senate and check senator's phones? Do they go to the financial district and look at trader's phones for signs of insider trading?

This is at least profiling or a discriminatory style of policing. They go to areas that have "those people" (whatever that means for this context) and do their policing there, avoiding the rich & powerful.

It's also a digital strip search in the street. If this is a valid style of policing, why not just digitally search everyone's phones NSA-style? Could it be that NSA-style wouldn't be discriminatory enough (a rich person might get caught)? Could it be that the psychological effects on the policed population are one of the motivations?

I hope that you're trolling, but since that's pretty uncharacteristic on this site, I'll answer you seriously.

Individual privacy, to start. The concept of probable cause to search someone is a concept found in most modern governments. Your communications to other parties privately are none of the government's business. It's an authoritarian measure that assumes guilt without suspicion. As others say, it will often have a racial or cultural component too, and at the very least a class one. People that look and act like the police would tend to be less subject to searches.

Apart from violating privacy, instilling a culture of fear thereby impacting people's right to free speech and free organization, which is a cornerstone of democracy, making people fearful of saying anything against the government or the police even in private conversation, nothing whatsoever.

Apart from power abuse, privacy, estaablishing a police state, and fucking over democracy, none...

A series of revolutions were fought to prevent this kind of abuse.

In the US, it's the fourth item in the Bill of Rights, but that's just a piece of paper, nothing worth fighting for...