Can’t mobOSes disable all functionality on movement above X/mph —perhaps allow it only if another device is in proximity (such as passenger presence, in public transit, etc), except for hands-free voice calls?
It seems like there's always corner cases that aren't considered (in your proposal above, what if the navigator doesn't have a phone because they're a child, or because their phone ran out of batteries? What happens when the sensors/algorithms are wrong about how fast we're going? What happens when the sensors are wrong about whether or not there's another device? What if that second device keeps disappearing and re-apparing while somebody tries to do a multiple step operation?) ... Trying to build some water-tight mechanism to keep us out of trouble but also with access to full functionality "when we can use it responsibly" is an endless rabbit hole.
IMO it feels like a systemic problem asking for a systemic solution. Whether we think that solution is self-driving cars, rail travel, walkable cities, or taxis probably says as much about our politics as anything else though.
Better option is to roll out the phone detection cameras and hand out 10 year license suspensions.
That’s on you. Like almost everyone over the age of 50, I learnt to drive before mobile phones and GPS, and it was fine. Paper maps and street directories worked well enough. Getting lost was uncommon, and no big deal.
Your phone isn't the state.