Re: but an incoming call takes over the screen
But with Windows Phone, once the call has ended, the previous display comes back. As does Android - or certainly if you're using the Drivemode app.
I've just tried the ACs setup and get the same result. Once the Google Search Screen pops up, it won't go away. Saying "Thank you" cancels the search but leaves the screen up, so if you were to be relying on your satnav, you'd need to touch the screen which can be interesting at 70mph.
Just a thought, AC, but maybe look at Macros ? See if you can setup a macro to close the search screen from a voice command.
As we are seeing with Alexa, OK Google, SIri, and Cortana, voice control is starting to be big. Not because it's gimmicky, but because people like my boss - who is getting on for 70 - won't give up their iShiny until they're dead ...