You sure about that? because if it's Google, that particular method of doing this would be easily discovered.
Also, the scary part isn't that they could do this by listening to your phone, the scary part is that they DON'T need to listen to your phone to do exactly that. Much easier to identify multiple devices coming from the same network (both physical and social), and then figuring out query interests, and then send ads down the same pipelines.
That’s exactly why I have my Garmin Descent.
It’s a dive computer, with basic smart watch features like notifications and general health tracking which are the only ones I need.
I happily paid 1k for it.