See if there’s a solar charger that works with your phone. It can be strapped to your trunk rack to make use of the sun while you are riding. Also, last year or two there’s been a portable station set up for lap tops/email check ins. Carry charger cable to plug your phone into computer while using computer.
The multiplug outlet was a good suggestion for sharing scarce outlets.
You could also set up check in times, and leave your phone off rest of time. But keep in mind that cell service will be overloaded or scarce in some rural parts of the state. If you are with a group of riders and plan to use your phone to keep in touch on the ride, you might be better off in buying sets of 20 mile walkie talkies to use for communicating back and forth on the road.