phoenix prices fell 9 6 cents last week averaging $ 2 42 a gallon beating out the national average of $ 2 57 a gallon according to gasbuddy com mariana godoy puts regular unleaded gas in her van for $ 1 99 cash at the valero gas station at 20th st and osborn in phoenix monday morning december 15 2014hoenix prices fell 9 6 cents last week averaging $ 2 42 a gallon beating out the national average of $ 2 57 a gallon according to gasbuddy com the national average has dropped 67 cents a gallon since last year