PHX isn’t a big connecting hub. Even AA has 60% of its passengers O and D. WN is like 80% I believe. WN has declared they intend to grow in PHX, DEN, and BNA. If AA draws down PHX, I believe WN will add flights. It won’t be 1:1 but there isn’t a whole lot of connecting traffic to begin with.
That's assuming WN has the ability to grow. Their growth has been extremely constrained for the past few years. Once the MAX returns to service, it will help, but honestly it won't put them that much further ahead of where they were before they retired the classics. They've got a big network, so they'll probably focus their growth initially on where they feel they can be most profitable. That may or may not include PHX in their growth plans for a while.
There are only a few remaining WN destinations in the contiguous U.S. without nonstop service out of PHX on WN that have nonstop service out of PHX on airlines such as BOS, CLT, GRR, LBB, MAF, TUS, DCA, and IAD.
TUS is too close to PHX for WN to consider serving TUS nonstop from PHX with TUS being only 110 miles from PHX. WN also already offers 1-stop connecting service to TUS from SEA, PDX, GEG, BOI, RNO, OAK, SJC, SFO, SMF, and SLC through LAS or LAX. There is no need for WN to operate PHX-TUS nonstop service with WN being able to connect passengers to TUS through LAX, LAS, DEN, and MDW.
WN re-adding PHX-BOS nonstop service might be a possibility as WN was able to fill PHX-BOS nonstop flights back when WN operated PHX-BOS nonstop service. WN also had better load factors on BOS-PHX in 2011 and 2012 than it did on BOS-ATL/CMH/IND/MCI/MKE in 2019, with WN having over 90% load factors on the PHX-BOS route in 2011 and 2012.
Even with PHX and CLT both being AA hubs and former US hubs, WN adding PHX-CLT nonstop service is a possibility with CLT being one of the top destinations that WN doesn't currently serve nonstop out of CLT and with Greater Charlotte being the third largest metro area in the contiguous U.S. (after NYC and Greater Boston) that doesn't currently have nonstop service out of PHX on WN.
WN is unlikely to add PHX-LBB and PHX-MAF nonstop service with LBB and MAF both being in smaller markets than any of the contiguous U.S. markets that WN currently serves nonstop from PHX. WN is also dropping DEN-LBB nonstop service due to load factors being much weaker on DEN-LBB than on most of the other WN nonstop routes out of DEN.
While AA has nonstop service to DCA from PHX due to beyond-perimeter slot exceptions, WN adding PHX-DCA nonstop service will not happen without WN acquiring extra DCA beyond-perimeter slot exemptions as PHX is located outside of the DCA perimeter.
While BWI is close enough to Downtown DC for those traveling to Downtown DC from Greater Phoenix, WN adding PHX-IAD nonstop service might be a possibility with DCA being perimeter-restricted, WN unable to serve DCA nonstop from PHX without acquiring extra beyond-perimeter slot exemptions, and IAD being almost 60 miles west of BWI.
WN adding PHX-GRR nonstop service might be a possibility if AA drops PHX-GRR nonstop service as AA had been able to make GRR-PHX nonstop service work seasonally before the COVID-19 pandemic. WN was also able to make daily nonstop service work to MCO, TPA, and RSW from GRR on a seasonal basis (at least before the COVID-19 pandemic), and WN also has a FF base in Greater Phoenix and Southern California to support possible nonstop service to GRR from PHX.
The return of daily WN nonstop service to CVG from PHX is also a possibility with AA and F9 both having already discontinued CVG-PHX nonstop service, with AA not resuming CVG-PHX nonstop service in December 2020, and with WN being able to make daily CVG-PHX nonstop service work in Spring 2018 and Spring 2019.