The problem isn’t that your phone is listening to you. It’s worse than that. The problem is that your phone knows where you are, on the backend, it knows who your friends are, and what they recently bought. If friend hadn’t mentioned the air purifier, you’d see the same ads; you just wouldn’t know.
Someone in my office today mentioned the brand of our office air purifier… and now FB is pushing ads for that brand of air purifier. It’s actually terrifying how our phones quite literally listen to us. (She says, typing from a phone that listens to us 🙃)