I haven't read all the responses, but here's my advice:
Find a map-book of the area you're going to be delivering, preferably one that has all the towns adjacent to your delivery area (if you bid a route, never mind, but if you're cover, you'll need those maps sooner rather than later).
Cut the pages out, 'laminate' them with clear packing tape (both sides), and keep them in your work bag.
Using the phone to check addresses is useful in a pinch, but honestly, you'll waste so much time with your phone, and your battery will die, etc.
With a map in front of you, you'll 'get the big picture'.
If you do it good with the packing tape, your map will survive coffee spills, you can fold it up, you can slide it in the seam of the plate that covers the instrument panel - easy viewing, etc.
Also, as others have posted, if you know the area you're going to be delivering to, it is quite useful to spend a couple hours on a Saturday driving the area.
Looking at the phone only gives you your next stop...looking at a paper map gives you the depth and breadth of the entire route...
You'll learn the traffic patterns (schools getting out, five o'clock traffic when everyone's leaving work, etc...)
Like Upstate says, work smarter, not harder.