Google has an option where you can download maps for a very large area to you phone.  Pretty sure you can download almost a whole state.  Staying with the phone for GPS helps me stay current with new roads and road closures, Road construction, and if you use apps like Waze for directions you get a LOT more fluid information as you travel.  Ex. speed traps, speed cameras and my all time favorite towing, Road hazards!!  Its nice to know a mile in advance when I'm heading for some trouble.     Of course all this is dependent on other drivers reporting the info.  There is much more info in heavily traveled areas than there is out in the stick.