These days, a smart phone is a perfectly good navigational tool, as long as you are using a high-quality, dedicated hiking app. The ability to see your location on a topographical map in real time is a marvel that explorers of old would have been amazed by.
However, technology is fallible and batteries can die. We would always recommend also carrying a map and compass and knowing how to use them, as well as having a navigational app. It's also a good idea to bring a power pack so that you can charge your phone, should it be running out of juice.