Wire ratings in very hot attics, e.g. Phoenix where they go to 180F?
Fix the issue at its source: the deficient attic

An attic that is hitting those temperatures throughout, even in a hot climate such as Phoenix, has a design flaw.  Either the ceiling plane needs to be air-sealed and insulated to allow the attic to be vented at the soffits and ridge to provide convection cooling of the space, or the underside of the roof deck needs to be air-sealed and insulated, forming a hot roof, to allow the attic to be conditioned and treated as interior space.

With proper venting, the attic should stay closer to 120&deg;F (~50&deg;C) worst-case at the top of the joist space, which is where most of the wiring lives in any case.  Of course, in a conditioned hot roof system, the attic will be kept at living-space temperatures instead; this is vastly superior to even a vented attic when there is equipment and ductwork in the attic, not just the occasional cable or vent pipe.  "Hot roofs" do have the downside that they can put more stress on temperature-sensitive roofing materials in hot climates, though, so there is that to keep in mind as well.

If fixing the attic isn't an option, then one could bury the wires in insulation given that they are at or near the joist space, but this does pose downsides for future maintenance.