The blaze — which police say was set by 29-year-old Matthew Egler — happened in the early morning hours Friday near Central Avenue and Thomas Road, causing "substantial damage to the building," Phoenix police said in a statement on Wednesday.
In a tweet announcing the arson suspect's arrest, Phoenix police posted surveillance video of flames erupting at the building and a man calmly walking away from the fire, stopping briefly to turn around and look at the fresh blaze, before getting into a parked car.
It wasn't immediately clear if Egler had hired an attorney or when his first court appearance would be.
Arizona has been reliably red for decades, having voted for just two Democratic presidential nominees — Bill Clinton in 1996 and Harry S. Truman in 1948 — since Franklin D. Roosevelt left office.
But this November, Arizona will be a crucial state for control of the White House and U.S. Senate. President Donald Trump and former Vice President Joe Biden are in a close race for the state's 11 electoral votes, while appointed Sen. Martha McSally is in a difficult contest against Democratic nominee Mark Kelly.