Most of my friends pronounce it "fuh" (as in "what the fu**?" [I know it's crude, but this was how I was taught to remember how to pronounce it, lol]).
However, I have since heard it pronounced like "faux". I live on the West Coast of the US and the first person I heard pronounce like "faux" lived on the East Coast, so initially I thought that perhaps it was just an East Coast vs. West Coast difference, but I have since heard it pronounced "faux" on the West Coast, as well.
So, in an effort to figure out the correct pronunciation, I went to wikipedia, and found this, which has a pronunciation that you can listen to, which sounds like "fa".
So now I am even more confused! I don't want to sound like a moron when I tell someone that I want to go out for pho, so I'm hoping you wonderful people can help me out! :-)