Gina - I am not the expert with potatoes, but I do know that Bone meal supplies P (phosphorous) which helps in root development. A high nitrogen fertilizer is good for lots of green leafy growth, which is not what you need with potatoes. So look for something that is low in N, higher in P & K.
Egg shells take a year or two to break down and make their calcium available to the plants, so adding them when planting doesn't make much sense to me. Toss them in your compost pile. I don't know that extra calcium is a must for potatoes anyway.
I know nothing about gardening in AZ, but in WI potatoes are planted as early as possible (when the ground thaws) I'm not sure how they will fare in AZ summers. Sweet potatoes like the heat.
