You can disable those. The thing is: smartphones are more than dumb boxes that listen to you all the time. So you don't want to remove them completely from your life, yet still want to keep your privacy.
You can disable a Google Home device just as easily, and the rest of your comment is just you declaring by fiat that phones are OK because you personally find them useful, and the home devices are bad because you personally don't find them useful.
If someone finds their home device to be "more than a dumb box" and doesn't want to remove it from their life, you're at an impasse. No one granted you the authority to just decide where everyone else gets to draw their own personal line.
Those are for calls. They need a microphone, you cannot do calls without that.
I'd argue that those (should not) transmit audio data to any random company, but then I've never understood what Google Now/Google Assist or whatever it's called nor what Siri is about..