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?
Evidence is simply a word to describe the artifacts that one wishes to use to support their case. There’s not some gate-kept process to “become evidence”.
After they get it when they are authorized to get it. You cannot point at random things and call them evidence. For instance, I can take a dump and flush it, despite law enforcement's assertion that my stool is evidence in some imaginary crime.
Yes, when they are authorized to make a drug bust. And that's assuming they catch him before he flushes, i.e., get the drugs. Otherwise, what are they going to say? He is a drug dealer because we heard the flush? Or let's say they are doing a missing person's search and hear the flush. What now? We came looking for a missing person, but heard the flush, so there were drugs whose evidence he destroyed?
Yes, absolutely. Something can be evidence if the police haven’t even seen it at all.
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.
The prosecutor can argue that you violated some laws, but they will have to convince a jury beyond a reasonable doubt of that. And they will need a lot more than "I heard the shredder" to convict you. In an overall case, the shredding can be a piece of the puzzle. Shredding, standing alone, is not a crime, nor is shredding as a general matter tampering with evidence.