Real suggestions for the OP:
If you have a bunch of short sleeve jerseys already, just get arm warmers. If you have massive arms be very careful with your selection... a lot of them run quite small. I'm 6' 175 with slim arms and I can't hardly wear Nashbar's cheap-o arm warmers in size large they're so fricken tight.
It is also nice to have at least one longsleeve jersey. If you're going to ride below 50 I'd get thermal. 50-55 you can use standard jersey material. On top of that if you need you can layer a windbreaker, and I highly suggest vented or zippered armpits.
I wear tights below 50, maybe 55 if it's really windy. Anyway, I would do these things because Phoenix is too damn hot to ride during the summer, so it seems like you ought to take advantage of the mild winter.