~20% of the Phoenix labor force is in construction.

And a large fraction of the construction labor is illegal aliens, who are:
  • Much cheaper than US labor, thus driving the construction boom.
  • Culturally alien and more prone to crime, thus increasing the attractiveness of "safe, distant" communities.
  • Directly driving the explosion of population which is served by the construction.
If you fenced off the border and deported illegals even half-heartedly, this problem would end.
You don't have to deport them. When the dollar stops being overvalued, the remittances they send home will become almost worthless and they will go home by themselves.