I'm still a little confused by the OP's assumption that he's a "tech-illiterate old guy". He's undoubtedly been using secure electronic communication systems for his entire career, and is certainly well-aware of the risks involved with compromised information. He's definitely more clued in than the amateurs who usually get this kind of government gig.

As you say, though, that makes him more culpable if it turns out he has actually been using the phone. But my money says he hasn't been.