In the past few years, we have covered plenty of decent solar chargers for iPhone here. The SunTray Solar Side Table is also worth a look. It connects to your beach chair and has dual USB ports to charge your smartphones. It comes with a cup holder as well as a non-slip surface for your device.
You can install and remove this solar charging side table in a flash. It works with any folding chair with a pole of 2.75-3″. This table measures 14”L x 8”W x 0.75”H[where to get it]