I have a Zumo 660 that came with my RT-L, yes I agree with you guys that it's really hard to see in bright daylight. Using your phone as GPS is excellent idea and it would make it easier if your phone has OLED screen instead of LCD. All you have to do is preload your destination at home - I use google Maps on my iPhone 12 - or wherever you have wifi then your phone will work even if you don't have cell signal.
Ryde Safe and Cheers.