Gaia GPS is still my go to after all these years (
Post from 2012) It has only gotten better with time. My phone is my primary GPS for just about everything, I do have a Garmin Fenix 5X+ but normally use it as a adjunct to my iPhone or iPad.
Avenza Maps is another phone/tablet based mapping app that is improving consistently as well. Not quite as versatile as GAIA GPS; but it has some additional features that make it a good option for some applications and it has become the standard mapping app for wildland firefighting. On most wildland fires I use the two app simultaneously