Yes this is different than when law enforcement serve a warrant and the defendant wipes his computer before the agents can get a hold of it. In that case the warrant covers what you destroyed as evidence.
Though during traffic stops, if a defendant disposes of his drugs while on the run, that can also carry a charge of destroying evidence even though no warrant was issued.
IANAL
Destroying evidence is a crime, regardless of any warrant.
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?