What makes you think the raw audio stream needs to be sent anywhere. Modern phones are capable of doing keyword extraction on-device.
This conspiracy theory has been around for a lot longer than phone hardware has been capable of doing that.
The Chrome Browser can transcribe audio into text, with what I consider good accuracy. It's well out of the realm of a conspiracy theory when it's been demonstrable for a couple decades.
Don't forget energy usage. The phone would need to be on high power mode all the time to run those kinds of algorithms. There's a reason "Hey Siri" has dedicated low-power hardware - it means it can work without burning through the battery.
> it can work without burning through the battery.
It can work by burning through the battery. When you have a browser open or any number of apps, some of them are certainly detecting.
You need to know what keywords to listen for before discarding the audio data. An advertising giant might know but a government doesn't.