What metric are you using to call Phoenix the 5th largest US City?
Census metrics estimate the metro area at 11th in 2024 and
BTS data also puts PHX airport 11th (down from 10th in prior years) in terms of passenger Enplanements. A high volume of that is connecting traffic vs O&D.
Cities and Metro Areas can be drastically different in size. Phoenix is the “fifth largest city” by population…and also I still see it at 10th largest Metro by population. The difference is the city is less than a third of the Metro total.
As for O&D, that’s not a bad thing, but makes
PHX an unlikely play as the SoCal and DEN and Texas hubs are close (in flying terms).