“When you ask Google Assistant or Siri to find something, this information is used for online advertising. It’s no different from typing something into Google Search. If you’re looking for car dealerships in your city, related ads will start chasing you across the internet. In a way, a virtual assistant is just another search engine.”
How to test your phone:
Select a good topic. It should be something that couldn’t be associated with your personality, something you never talk about.
Isolate the topic from your phone. Do not use your phone or any other device to search for information on this topic. The best way to do so is to think of it in your head. Make sure you have never Googled this topic.