I use the sun and the stars
I actually don't use one locally but especially for dual sporting I have a second phone, Samsung S7 Active taht I picked up on ebay for $30 because it has a pink line on the screen. I use an app onX Offroad, they have other variations, anyway you can download for offline use. The bonus is if my phone falls off or I dump the bike and break it or something I'm only out $30
I was thinking the exact same thing with considering an old phone I have laying around - if I destroy it my feelings won't be too hurt!
The old phone in question is my iPhone 6s which survived falling out of my pocket on the highway at 80 mph and worked for another year with a cracked screen before I got around to getting the screen replaced - at no cost because it turned out to fall within a month of prodcution where Apple had issues with the glass they used for their phones at the time.
And I'm going to check out the app onX Offroad!