The implication they are making is that the person _intended_ to destroy potential evidence on the phone. That the person felt there was evidence on it that needed to be destroyed to hide a crime.

IMO, even if that's actually illegal, there's zero way to prove it that the fifth amendment doesn't address.

The 5th has been distorted by the courts so much, that I wouldn't assume any novel interpretation would stand (and wiping data to avoid self-implicating is novel).

For instance, apparently answering questions up until a point at which you don't severely threatens your legal ability to invoke the 5th.