Sorry I can't help you with your palo verde...

But I would suggest trying the Arizona Gardening Forum, that looks like a great active forum that is obviously more pertinent to your location (lots of gardeners from Phoenix). I'm sorry to say that this forum is pretty much dead, and seems to be mostly NM folks when it is used.

Good luck

I don't know if Phoenix had the same hard freeze this past Feb. that we had here in NM. But if so, you might be seeing freeze damage. Your mentioning that it didn't flower, spare foliage and the presence of brown twigs might be evidence too.
You didn't say how much water you've been giving it but you may have drowned it. Palo's are quit xeric and an established one should be able, for the most part, to get by on normal rainfall. If I remember correctly they are native to the Sonora desert.
With the hard freeze this past winter those of us over here in southern NM discovered that "Desert Museum" palo verde is less cold hardy the the species. Not that the species is anything to boast about.
Is the tree dead? Is everything above ground that funny pumpkin brown color they turn? If so, cut it off at the ground and see if it comes back from the root. It probably won't be "Desert Museum" but at least it's a palo. Or just replace the plant.

Re: posting pictures
Do you have an account with an online photo site like Photobucket or Flickr? You can't post photos directly to GardenWeb but you can through one of those sites. I use Photobucket myself.

Re: Is this forum dead?
I think it goes in waves although it does seem to be used mostly by NM people. Maybe we're just more into water-wise gardening than others.