Not sure what kind of phone you use, but on a sunny day I can't see the screen on mine well enough to read it.

I use a Garmin GPS. It is readable in full sun with the backlight turned off. I have the most trouble with mine when the sun is low in the sky in early morning or late evening, then the angle of sunlight is low enough that it does not light up the screen very well and ambient light is still bright enough that the screen backlight is not as bright as I would have liked. But it is still readable, but I might have to stop to be able to read it well.

My Android phone, I use the Maps.Me app and the Komoots app. I use a Garmin on my handlebar while cycling and mostly use the Garmin for routing. I use the phone apps when sitting in the campsite to compare different routes if I did not like the looks of the route that my Garmin suggested.

Maps.Me, I load the maps on wifi and can use them off line. It has routing by car or by bike. Last time I tried the bike routing (months ago, maybe it is better now?) the bike routing was really poor, I dd not use it.

Komoots, I need a data connection to use that, or wifi. I only used that for routing when I was unsure of route.

In all cases, Garmin GPS, Maps.Me or Komoots, sometimes a local road on a paper map works better. When I decided to use a Maps.Me or Komoots route, I did not have the software or programming smarts to transfer a route to my Garmin, instead I would pick some points along the route that I wanted to take and tell the Garmin to go to those specific points, in which case I used the Garmin routing for shorter segments of where I wanted to go that day.

Regarding buying or accumulating free maps, and paper stuff in general, a lot of paper weighs a ton. I try to find good paper maps for each state (or province or country) that I am going in, but I try to avoid accumulating too much paper.

My Garmin, there are plenty of internet sources of maps, I download them to my computer, upzip them, install on my Garmin GPS. I do all that before I leave home for a trip.

I did a four week bike tour in Iceland and a five week tour in Canadian Maritimes, both times I did not have a local sim card for my phone. Thus, my phone was only good as a wifi device. My point is that you can get by pretty well with poor data coverage if you planned ahead.

I also have Google Voice with a phone number, Hangouts and Hangouts Dialer apps on my Android phone, with that I can make phone calls where I have wifi even if I do not have phone coverage. It is hard to call me with that, but at least i can make calls if I need to. I have used restaurant wifi to make phone calls that way.