Most of the places have been covered. Since you are shooting with medium format and Phase One, I would rank them:
1) Bear Images in Palo Alto
-- give them a call, talk to Diane to get on the mailing list for their Phase One seminars, etc. Let her know that you are a Phase One owner and what your interests are. She can answer many P1 questions, since she owns one herself and shoots studio fine art.
The owners are very experienced with Phase One as they have set up archive and studio projects all over the world.
There are full-line Phase One, Mamiya and Canon digital dealers. They still have NIB Contax gear.
2) Calumet (18th & Bryant)
They have all the studio gear, film, paper, bags, small parts, etc. you might need in a shop that is "local". I haven't dealt with their pro digital people in a few years. They are helpful, but clearly not as knowledgeable as Bear.
3) Keeble & Shuchat in Palo Alto
Probably one of the last full-line photo dealers in the Bay Area. They have two stores:
a. Consumer - Canon, Leica, Nikon, Olympus, Sony digital cameras, books, tripods, etc. If you need it, they probably have it.
b. Professional - Medium & large Format, Hasselblad, Mamiya; Hasselblad & Leaf digital; studio gear, used equipment & rentals.
The prices are retail, but if you are a professional and build report, they do offer concessions.
As for rentals in the City, I'll defer to the above posts.
Hope this helps.
NGOphotographer