Getting over a downhill phobia
Easy answer....is to recover gradually. My experience has been in S.F., Seattle, and now Portland. All of which are hilly cities. Plus a lot of riding on mountain roads. So, I totally relate to your situation. ...and it's not always an easy answer.

After spooky near-misses, and a few crashes...here's what I do to get my mojo back.


Find some significant, low-traffic hills where you can just have fun and enjoy the exhilaration on the downhills. You don't want this to be too steep and curvy, but you do want speed. The goal here is to comfortably enjoy the descent and ride it safely.
After that, move up to a more congested and/or curvy hilly area and do the same thing.
Once you're comfortable with fast, downhill riding, you can get into some traffic. But now you have "city riding" in the scenario. You must balance your downhill skills with your city skills.


That being said, I have watched some messengers scarily bomb down Nob Hill. Personally, I don't need to duplicate their endeavors; however, one can do those hills without riding the brakes.