great topic and for good reason, who wants to get lost!
This has come up about 20 times at least (I wish I could just link my responses, lol)
I'm using gaia app on my iphone, but gaia has been available for android for a while, I think.
I've experienced several apps and imo this is the best one, hands down. note: I pay for the premium membership which gives me download access to hundreds of maps, including NATGEO TRAIL ILLUSTRATED, which by themselves is worth the price of admission!
I advise folks to skip getting a stand alone gps unit, and since you are going to take your phone anyway, use that as a 100% reliable gps/map/navaid unit.
Let me explain...no there is too much...let me sum up;
The phone is better because the screen is MUCH LARGER and easier to read and work with.
Put your phone on airplane mode to save battery, yes the gps works in airplane mode.
download your maps before you leave home and lose service.
as a bonus: create a 'route' - or your trip, on third party software, (as a gpx file) I highly recommend caltopo.com, then send that to your phone, that will magically appear as an overlay on your downloaded map in gaia, so you can match your progress against your intended plan.
there will be comments about battery life, water proofing, tracking (gaia does that and everything else you could ever think of), taking a paper map, knowing how to use a paper map...yada yada yada.
Your screen on the phone is going to be about 5 times larger than all but the most expensive gps unit - and you are already taking your phone!!!! do you really need two devices!