Why leave it turned on? The inside of the car in daylight will be warmer than the outside temp. No problem.
I'd be worried about summer. The car will get broiling hot inside.....
I totally agree with "Givmeabrek" especially the last part, think about how you are going to keep it cool in the summer. I'm now retired, but when I was working I was allowed to carry my iPhone with me and I've done so since the iPhone 3GS. Since the work I did required me to be outside quite a bit in winter it meant that at times I used it in -0º F weather, and I never had a problem except the battery going down a bit faster on the colder days. A recharge during lunch took care of that.
I was more concerned about the effects of hot weather than cold. No electronics like hot weather, and there were many times when I was carrying it when the temp was above 100ºF but again, although I was concerned, the heat did not seem to bother the phone at all.
Remember that your car will be a bit warmer inside in winter, than the outside temp, and much hotter inside in summer. Leave it on the dash even while driving in summer, and you might regret having done that. The dash especially in a car that has a dark colored one can get a lot hotter than you think even while driving on a warm summer day with the A/C on. One reason why I don't use those sticky pads to hold my phone in place on the dash.
I think that all said and done, any smartphone can tolerate low or high temps much better than the owner. Temps that would be realistically harmful to the phone would be very bad for the owner.