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.
Also, have you ever been butt-dialed by someone? 99% of the time you can't understand a single word, let alone enough to make any semantic sense out of.
If it's trying to figure out if you're watching Stranger Things it can look for when your stationary at home and just needs to record a few seconds at a time every few minutes. I don't know how the fingerprinting works. It might be able to run locally and not use a ton of power. We're talking Shazam, not full text transcription.
And do what? Sentiment analysis on the conversation you were having?
Remember semantically aware models are still fairly new and even they lack the context for a particular field of text. That's something even the new fancy LLMs struggle with.
Unnecessary when there's way better targeted models trained on years of data that people willingly send as part of everyday smartphone use.
Sentiment analysis on the conversation you were having?
Among other things, sure. More simply, keyword analysis.
Remember semantically aware models are still fairly new and even they lack the context for a particular field of text.
All of these "models" are useless garbage but it doesn't stop them from trying to absolutely cram them everywhere they can.
Unnecessary
None of what they do is "necessary". They could just ask you what your relevant interests are and you could tell them, but they do it anyway. They go to great lengths for any seemingly insignificant amount of data they can get their hands on.