I accidentally left my iPhone 5 a few hours in direct sun and it overheated. Obviously I put it in shade to cool down but my question is will there be any significant damage? Long term? It was really hot when I found it.
If you cooled it down, then the problem is resolved for now and there is nothing more you can do. Try to avoid doing that again as this will slowly move from the short term effects to long term ones.
Short Term Effects of Overheating
Long Term Effects of Overheating
When the iPhone overheats, Apple also claims that you might experience these (more extreme) results:
To stop this from happening, try and turn your iPhone so that the screen is facing down. This will help it avoid contact with the sun. If you have a case, that will be better because the sun will be hitting the case instead of the phone directly.
Starting at 40 Celsius (104 F) we think it is very hot.
At 50-60C (122 F-140 F) it is burning hot and we could not touch it.
Above that we actually get burned.
So you phone could have not been hotter then the outside temperature in the Sun (probably 40-45 C max if you live in Arizona).
Still that is hot and could have impact on your battery life.
Preventive methods are:
Using a white color phone housing.
Using the reflective phone housing.
In both case the temperature would be lower by as much as 10 C. (due to the reflection).