Can I charge a phone while hiking?

Yes, by strapping a panel to your pack's exterior. Output will vary as your angle to the sun changes. A power bank as a buffer between panel and phone provides more consistent charging.

How many watts do I need to charge a phone?

A modern phone needs about 15-20Wh per full charge. A 20W panel produces this in 1.5-2 hours of direct sun. A 10W panel takes 3-4 hours.

Best Solar Panel Chargers for Backpacking