I used to work for a mobile advertiser, and we installed hella bloatware on phones.
This idea was floated a couple times but was deemed not very effective cause you'd have to store and process hours and hours of audio data that didn't tell us much more than just having a week or so of GPS data, your Facebook profile, and your phone IMEI.
It's pretty easy to see if you're near a Popeyes and what other IMEIs are connecting to the same tower, extrapolate that to you being near your wife and you and your wife thinking about shit on the Popeyes menu.
Boom targeted ad/video for fried chicken.
The rest is general tech paranoia leading to Apophenia.
There's no microphones or cameras, it's just the already gigantic mountain of data anyone who uses a smartphone is constantly broadcasting getting ground through the big data machine that has been the pillar of all tech since the last recession.