"I don't think phones ring because we rely on our ears in times of danger. It's because hearing is one of the senses that doesn't require exclusive focus (you would not want to stare at your phone all day until it starts blinking, although in some offices they do)."
One could say the same about cars. Silent cars would require much more focus and no amount of adapting will change that.
I disagree. Take for instance a city like Amsterdam (or any other Dutch city for that matter). People ride bikes there. Lots of bikes. Fast bikes. When you go there for the first time, you better make sure you walk on the right side of the side walk, or else you're actually in danger of getting run over - you're just not used to them, and the bike lanes often are on the side walks.
But you do get used to that - you simply start looking out more carefully.
I see no reason why it should be different with cars, especially since you would probably hear even a silent car more easily than a bike.
One could say the same about cars. Silent cars would require much more focus and no amount of adapting will change that.