TL:DR: They don’t need to listen to you. They already track “your metadata”

"To make it happen, Facebook would need to record everything your phone hears while it’s on,” Garcia-Martinez explained in 2017. “This is functionally equivalent to an always-on phone call from you to Facebook. Your average voice-over-internet call takes something like 24 kbps one way, which amounts to about 3 kBs of data per second. Assume you’ve got your phone on half the day, that’s about 130 MBs per day, per user. There are around 150 million daily active users in the US, so that’s about 20 petabytes per day, just in the US. To put that in perspective, Facebook’s entire data storage is ‘only’ about 300 petabytes, with a daily ingestion rate of about 600 terabytes.”

But there are scores of other data points the system has on you to determine what you should see at any given point. Not only does the system know exactly where you are at every moment, it knows who your friends are, what they are interested in, and who you are spending time with. It can track you across all your devices, log call and text metadata on Android phones, and even watch you write something that you end up deleting and never actually send.