Physically, there's constraint on what I am exposing. Digitally, it's my entire life. The bar for a search must be much higher to reflect that. Most people here are not used to dealing with a corrupt officer. Imagine a scenario where you own a property and the police officer next door desperately wants it and he finds a loop hole to block your access to the street (and does more horrible things to get you to vacate your house). Now imagine what he'll do if he had your phone and work backwards from there - even innocent things like a flirty message with someone can potentially ruin someone's life - it doesn't have to be illegal.
The justice system and separation of powers acts as checks and balances from anyone (good or bad) being harassed unless there's a strong reason why. Get a warrant with a limited scope and then do the search.
No need to imagine. There are innumerable cases over the years where cops have turned into stalkers backed by the power of the government when their girlfriends dump them. It happened to one of my ex-es, but I've seen it in newspapers dozens of times over the years.
The problem is that cops are still people. And people are often messy, emotional, irregular, obsessive, mean, or just have a bad day and need someone to take it out on.
Wetware will be wetware. All we can do is advocate for better training and smarter policies.
The justice system and separation of powers acts as checks and balances from anyone (good or bad) being harassed unless there's a strong reason why. Get a warrant with a limited scope and then do the search.