There are many anecdotes, and even I can think of a handful of times where I wondered the same. Officially, yes our phones are listening all of the time, but supposedly only for keywords for voice assistants, mostly.

Amazon, Google, and Facebook deny that they record all conversations, and Google even had users opt out of voice collection when accusations about these things first popped up.

It is likely that these companies have so much data about us and the people around us, that they are able to infer things that come up naturally in conversation with friends and family. For instance, they know when someone else in your vicinity searches for something. So, for example, when one of your friends searches for a movie that you talked about in conversation, these companies know to show you that movie's preview.

Still, I wouldn't be surprised if at least one of these companies is doing something shady with audio data.