FWIW CMG doesn't claim that this is from smartphones, and instead ambiguously refers to smart home devices (and I would be shocked if say, Google allowed a third party to access its microphones for Google Home devices). Similarly, there is no way that the FB app is doing this (for one thing, you'd see the microphone icon on your OS) — the "FB partner" here just means FB buys some rolled-up marketing info from them, probably with zero idea where the data comes from.
If I had to guess, I'd bet this is from shady smart TV manufacturers, who have a long history of spying on their users and selling that data.
I have no evidence that CMG is doing this today. However the archived page [0] from CMG’s site describing “Active Listening” specifically mentioned smart phones. From the page:
“Active Listening begins and is analyzed via AI to detect pertinent conversations via smartphones, smart tvs and other devices.”
If I had to guess, I'd bet this is from shady smart TV manufacturers, who have a long history of spying on their users and selling that data.