Alaska Airlines, United, and Delta have round-trip flights from Phoenix (PHX) to Anchorage or Fairbanks (ANC, FAI) for $236-$279. Anchorage flights August to December, nonstop. Fairbanks flights August to September. Weekends available. No Christmas dates available.
Some small OTAs on Skyscanner have this for cheaper than the airline. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.