The following comments are in the context of traffic engineering, road capacity, and automobile flow. They're not in regard to land use intensities:

Road hierarchies [local, collector, arterial] is a strongly suburban concept. Downtown Phoenix would be better off without it. (Some will argue that it doesn't even make sense for suburbs.)

Road hierarchies increase traffic congestion by underutilizing "lesser" roads. This might be sensible (or at least valued) in suburban areas where homes are expected to be isolated from traffic and commercial activity, but that doesn't translate sensibly to an urban environment such as Downtown Phoenix.

So insofar as right-of-way widths will allow, treat all roads in Downtown Phoenix the same for traffic purposes. (i.e. Roosevelt = McKinley = Adams = Lincoln = etc) -and- (5th Ave = 2nd Ave = Central = 1st St = 4th St = etc)