Phelps has 16 Olympic medals, 14 of them gold, making him the most-decorated male athlete in Olympic history. In 2008, he broke Mark Spitz's single Olympics record by winning eight golds in Beijing.
Phelps was also voted the Associated Press Male Athlete of the Year, and the Sports Illustrated Sportsman of the Year. He had also won the USOC award in 2004.
All-around gymnastics champion Nastia Liukin and swimmer Natalie Coughlin tied for the USOC SportsWoman of the Year award. Swimmer Erin Popovich was selected as Paralympian of the Year. The gold-medal-winning U.S. men's volleyball team was voted Team of the Year.
The results are based on votes from the national governing bodies for the Olympic, Pan American, Affiliated and Disabled Sports Organizations within the U.S. Olympic movement.
Some information for this report was provided by AP.