I live in MN, and if it’s cold out, I keep my phone next to my body somehow, like a pants pocket or inner jacket pocket in the chest area. This keeps the phone warm enough to work for a while at any temperature you would attempt to use a phone in (I don’t try to use my phone outside when it’s -20F because I don’t want to remove gloves, but 0F is fine) and if it’s too cold, you can rapidly warm it up by placing it between your legs/against your skin/etc.

In he summer, I don’t leave my phone in direct sunlight for extended periods or else it will overheat. Simply placing it in the shade or in a pocket prevents this. It usually only hits 100 here, so I don’t have experience with the 100-120F range and overheating.

Tl;dr Prevent your phone from reaching extreme temperatures and it will work fine.