I also agree that holding a conversation on a phone hands-free is distracting but, in the same way as talking with your passengers, at least you have your eyes on the road.
Eyes on the road, and mind on the road are quite different things as any victim of a SMIDSY can tell you.
Surely car and phone manufacturers can cooperate to ensure that mobile phones can't text at all and can't make calls work inside a motor vehicle unless they are linked to the ICE system?
No, it would be difficult. How does a phone know it is inside a motor vehicle? Speed of movement? Position on road? That would catch people not driving and possibly not in a vehicle. So some sort of signal generated by the car when it's in motion? Well, that would only be for new build cars so it be years before it would make an impact, and it would probably mean no phone use by a busy road side, and possibly in houses near the road.
You can't just block calls and text, you have to block data too as there are hundreds of ways to make calls and send texts that use data not voice or SMS. If you block data, then GPS won't work, vehicle tracking won't work, apps like Uber would have to shutdown etc.
Plus unless it was a worldwide thing, people would just start buying their phones from different markets that don't have the restrictions, or flashing their phones with software that doesn't.