Probably poisonous, or at least causing gastric distress. There are NO edible mushrooms that naturally grow in Phoenix.

If you have buried wood, or wood-based compost, they will grow.

You have to assume that any wild mushroom is bad for you to eat. The presence of mushrooms indicates that you have a fungal infection in your soil (mushrooms are only the visible portion of a much deeper problem, and they grow fast). I would cut back on your watering schedule since it doesn't take long for a fungal infection to spread around. Don't buy commercial fungicide products around your pants since they will fry your crop. A natural remedy is to mix one tablespoon of apple cider vinegar to one gallon of water to control the fungus.

sounds like you are way over watering if you're getting mushrooms...

Eltigre ... mushrooms are NOT an indication of a "fungal infection in the soil", and they do not need any remedies poured on them. They are not pathogenic to plants, and do not carry diseases. (trust me, I studied mycology in college).

They are indicative of some abundant source of rotting material - usually wood or wood chips buried in the bed - and may indicate you need to cut back on the watering.

There are no edible mushrooms in the low AZ desert ... most will not kill you, but they can make you feel really really bad.

http://www.tanelorn.us/data/mycology/myc_loc_des.htm

Here is a link that might be useful: AZ desert Mushrooms

Good info lazygardens. I had some mushrooms in the fall. In the last couple of months I have had this really interesting fungus called bird's nest. It looked just like this: http://www.backyardnature.net/f/birdnest.htm

Should I be concerned with it at all?

Yes there are wood chips in my soil, and also we are still fine tuning our watering schedule so some parts of the garden are probably too wet.

Those bird's nest fungi are COOL!!!!

Mushrooms are part of the natural decomposing process of wood. I pull them out when I see them to keep the pets and children from eating them, but they aren't going to damage anything.

Wood chips, yep. That's what it is. I've been pulling them and throwing them away as I see them (along with the mesquite tree seedlings that are popping up all over -- I should start a mesquite orchard). Note to self: Clean out all the debris/sift the soil before turning everything under next season! Sheesh.