There are two routes from Boise to Phoenix. One is 93 south out of Twin Falls, Idaho, while the other route is I-84 to I-15 through Salt lake city. Each has their own characteristic...93 is single la...
I would take 93 for that trip. Overnight in Ely. Do it about every year except to SoCal instead of Phoenix. I15 is longer and more traffic and nothing special for me.