I've had a driving phobia since I first got behind the wheel at 15. It's taken me a lot of baby steps to be able to drive and I still don't do highways or go downtown.
What helps me:
If there is a grocery store that you already drive to comfortably, find another business that is in close proximity and make it your goal to drive there too.
Make sure you know where you are going ahead of time. For me, this means I look stuff up on Google Maps and if I'm particularly nervous, I'll ask DH to show me the easiest way to drive there and we do a test run.
Get a GPS! I don't use mine all of the time but it's nice to know it's there so I can't really get lost.
Keep at it. Keep trying to add new places or areas to drive to. It's taken me almost 5 years to be able to drive to the dang mall but I finally did it.
Know thy back roads and pick times of the day to drive when traffic isn't so heavy.