Quick check with Google maps says the direct route is about 2000 mi while this route is about 2600. If you go by Phoenix you might as well go see Disneyland. Every 8 year old should get to go to Disneyland! (but I understand LA traffic might be the penalty)

Doesn't look to me like there's much choice in routing to avoid weather because different choices won't make much difference. Weather usually covers a large area. (at least the bad stuff seems to)