One thing I have learnt over the years of GPS stuff is you need an app that does not rely on the phone network, but then you may only be City based and you have no problems, but also I for example end up in many non Phone base reception areas and only rely on GPS based maps, so you also need to decide which App you select for your needs.
Don't ask me what maps I use because they are not basically suited for phone use, or your use.
Enjoy your outdoor life.
Mags