Can't speak to Garmin, but the Bolt downloads the routes that are created in RideWithGPS, Kamoots, etc... so the navigation is conducted soley by the head unit.

I think there is a mistaken assumption that since the Bolt connects to your phone via BT that it uses your phones resources while riding (ie at the same time). That is not the case. The BT connection is there only to setup your Bolt, to auto upload your rides AFTER it is complete, to download the routes you created in RWGPS/Kamoots, and software updates.

It does not require your phone to record your ride or to navigate.