|Don't expect a cell phone signal here.|
I am using an iPhone 5s, so not the newest, but I have noted that its GPS unit is about as good as my Garmin's . . . except that for geocaching, it is not so good, because geocaches are marked in hours/minutes/decimal minutes, and the built-in GPS reads hours/minutes/seconds.
Now there are decided geocaching apps that work fine, but they require a good cellular data feed, and when you are in a place like the Purgatory River canyon, you end up thinking, "What possesed me to leave the Garmin in the truck and bring just the phone?"
Bottom line: a dedicated GPS receiver does more stuff than a smartphone does. Using GPS sucks batteries dead, but it's a lot easier to swap in two more AA's than to carry a cell phone backup power source (although I have one of those too, solar-powered).