There are no outlets at your personal campsites unless you rent one of our tent/RV packages that explicitly include this feature. That being said, there will be portable charger rentals through chargeFUZE at the festival. Rentals cost $15 per day.
You will be happiest bringing a portable battery charger for your phone to use at your campsite and/or occasionally using your car to charge things (careful with your car battery though, and also be sure to watch where your car exhaust is pointing - carbon monoxide is no joke)