How often do you actually need to see the phone for directions? You aren't traveling at a high speed, so turns come slower than in a car. A constant view of a map and turn by turn directions are not really necessary. I also didn't grow up with turn by turn directions, though I did understand it can be helpful at time to be used to find a specific address, but on a bike tour, it is less necessary. My preference is for maps, but that is me. I did use my phone for my last tour, but I used WikiCamps and used their maps as basically a "paper" map, and not turn by turn directions.
Keep the phone in your handlebar bag, or somewhere else enclosed, until you really need turn by turn directions, then put it in your handlebar mount. You can also use a map pocket if your handlebar bag has one. That will keep it encased in plastic, and you can see it. I do that sometimes on a motorcycle, in a tank bag map pocket. I can still utilize the touch screen through the plastic.