I don't understand. If I got a call in my daughter's voice saying "Help! I'm being held for ransom! Send all the bitcoins!" And then I call her phone and she answers or she walks in the door having gotten home from school, how is anyone going to collect on that?
I might watch too many spy movies but maybe they wait for a time she will be away from her phone, like the camping trip she has been talking about for weeks or a school field trip that can be easily learned and googled from conversations about class or sports competitions based on googling team names. These are all things that are likely to come up in regular, routine conversation.
The real question is why you wouldn't already be terrified about having a microphone in your house that is open to the internet.
In your contrived scenario meant to defeat the premise, no, it won't work. However there are basically limitless ways this data could potentially be exploited. The point is they don't need to even do it now, it could happen any time. Data doesn't just go away.
