The problem
Voice assistants are genuinely useful and come with a microphone that is always on, an account, a cloud, and a company whose interests are not yours. For many households that trade is not worth it, so they go without the useful part.
What this does
Dial 555 and you are talking to Home Assistant’s Assist — your own automation, running on your own hardware, answering questions about your own house.
Why a phone is the right shape for this
It is a pull interface. Nothing is listening until you dial. That single property is the entire difference between this and a smart speaker, and it is not a setting anyone can change on you.
It also works from every room already, needs no new device, and is usable by someone who would never speak to a speaker in the corner.
Details worth knowing
It is optional and isolated. The hook lives on its own extension. If Home Assistant is down, the phone is exactly as good as it was before — the lobby, the ladders, and the ringing are untouched.
Your automation, your rules. Assist runs locally if you configure it locally. Nothing about this design requires a cloud, and the phone half certainly does not.