Hm but the drugs are only evidence because they're illegal? So the phone owner only destroyed evidence if the phone contained something illegal, but innocent until proben guilty?
The textbook tampering with evidence example is: drug dealer tries to flush the drugs when the police knock on the door.
But yeah, people tamper with evidence because they think they can get away with it. That doesn’t mean they always succeed in cleanly doing it without creating evidence of the tampering itself.
For example: the police think you are running a fraud scheme. They knock on your door. You shred a bunch of paper. The police wanted to see what was on the paper. You have violated the US law on tampering with evidence.