I think the native Claude and Codex apps already do this for free. They even have the voice input.
They currently don't have the ability to use a local session from your phone, and they only have voice input, not voice input and output for completely hands free usage.
alt Hacker News
They currently don't have the ability to use a local session from your phone, and they only have voice input, not voice input and output for completely hands free usage.