I had a Huawei phone about 3 years ago. It was an Android phone and I am a developer so I set up developer mode and installed a shell and snooped around everything on the phone. There was a small piece of software and a string in a file led me to a software company name when I Googled the string. That led me to some talk of a surveillance algorithm. I can't remember the details but I remember being amazed by the genius of the thing. They were essentially sweeping up metadata, things like who you call, how long, who you send SMS messages too. From that they would be able to map out a normal state of affairs, and whenever something disrupts that state, like if people in one city start to get upset because of a corrupt official, this would be noticeable like ripples in a pond. There is no way that they could be transmitting video from every phone or even audio. But they certainly can analyze the phone usage and send anomalies to a central site for analysis in context.