Older iPhone in a Lifeproof case (getting hard to find) or a newer waterproof one in a Quadlock case. Don’t fall for the trap of thinking you’ll never need to stop and faff with it en route again. Between cables, software, signal strength, mount and device, there’s a lot to fail in the adventure riding scenario. Less so road touring. I’ve gone back to making a rough mud map & sticking it in a zip lock bag for dirt riding.