I use Gaia. You don't need a phone signal to use it. Just download the maps at home before you leave. It's user friendly and the learning curve is pretty shallow. But there are downsides to any phone GPS app. Lots phone's displays wash out in the sun. On and extended trips, you will need to carry extra phone batteries (expensive) or some source of USB power. Most cell phones are not waterproof. I did use the cell as a GPS on several trips but for my needs a dedicated GPS unit works better.