City officials said that marked a 3.2 percent increase over the numbers recorded in March 2013 and was the first time the airport has seen more than 4 million passengers in a single month.
"Spring training, students on spring break, Arizona's great weather and our state's many attractions brought visitors to Phoenix in record numbers," said Phoenix Aviation Director Danny Murphy.
In the first three months of this year, the airport saw a 3.3 percent increase in passenger numbers compared to the same time period last year. April statistics for Sky Harbor are not yet available.
"Valley hotels and resorts saw a 2.9 percent increase in occupancy in March 2014 compared to the previous March," said Debbie Johnson, president and CEO of the Arizona Lodging & Tourism Association. "Tourists spend more than $19 billion every year in Arizona. An increase in the number of visitors to our state is good for everyone."