I'd recommend that you get a decent hand held GPS instead of trying to cache with a smart phone, unless of course your cell phone will provide GPS coordinates when out of cell range. If you are caching in the SW deserts, or mountainous areas, you will need a GPS that works when the cell tower is out of range.
If you get into caching much, you may want a GPS that you can download info into. Make sure your GPS shows coordinates rather than a map of where you should be. To find geocaches, you are gonna need to be extremely accurate.
My wife and I have been using the same old antique Garmin GPS12 XL which was one of the first "modern" GPS receivers. By todays standard, it's heavy, doesn't work as well as some of the new models, requires a serial bus to interface with a PC, eats batteries usually by lunch, but it has never let us down either as long as we carry spare batteries.
Though I haven't looked, I'm certain all the new GPS units are USB capable for up and downloading information. When you are shopping for GPS units, see how difficult it is to input new waypoints/destinations manually. How many will it store?
KISS - Keep is as simple as possible and you will enjoy your GPS and geocaching.
BTW - The SW desert was training ground for George Patton's WWII troops. There are lots of remote desert geocaches that are located near training areas that you still see where the camps were set up. One spot we found in the middle of nowhere was an area where troops spelled out in giant letters visible from the air "QUARTZSITE 11 MI" with an arrow pointing to the town of Quartzsite, AZ, There is also a compass rose laid out on the ground for lost pilots to get their bearings at the same site...
I wish it showed up better, but from Google Earth...