Will my iPhone 5C be OK if left in a hot car all day?

The company I work for has just enforced a strict no cell phone policy and installed a metal detector at the front entrance to prevent anyone from bringing a cell phone into the building.

I'm concerned with leaving my iPhone 5C in a hot car from 8:30AM - 5:00PM. Where I live, summer days are currently between 79-86 degrees F. I asked the security guard if he could hold my phone in his office during the day but he said he was told not to hold phones for people. The obvious answer here is to leave my phone at home, however my commute is about 1 hour one way, and I don't feel comfortable not having a cell phone in case of an emergency - what if I break down? Or simply what if a loved one needs to contact me. So what do I do? Is it safe to leave my iPhone in the car? Should I keep it in a lunch box with ice packs in my car (obviously in a dry zipped section of the lunch box)?

Leave the windows open an inch or so and leave the phone on the floor under the floor mats.

Good: leave it on the floor of the back seat, where direct sun won't hit it.

Better: use a white towel to make a "sunshade" in the back seat, and put the phone on the floor, under the sunshade.

With my experience, iPhones are pretty sensitive to temperatures. I think your lunch box idea is excellent, just be careful not to freeze the phone with all the ice.