Originally Posted by worwig
I think you will find two issues here.
One is that the phone itself generates a fair amount of heat, particularly when being charged and the screen turn up to overcome sunlight. So you need to get the heat OUT of the box.
The other is sun shining into the the box through the opening. Like sunlight into a car window, then being trapped inside. Again you need to get the heat OUT of the box.
I suspect aluminum would conduct the heat out to the cool breeze blowing over it much better then plastic. But then it may also kill the GPS and data radios too. :)
The aluminum would have to be in direct contact to serve as a heat sink.