"If you can handle eight gold medals, you can handle anything," Bush told the record-breaking medalist in a telephone call to Beijing from his Texas ranch.
Phelps won eight gold medals, eclipsing Mark Spitz's seven-gold performance at the 1972 Munich Games. Phelps now has an astonishing 14 golds in his career, five more than any Olympian ever.
In the call, Bush said he and first lady Laura Bush were thrilled by Phelps' achievement and that the swimmer had handled himself with "humility," White House spokesman Gordon Johndroe said.
"He told Michael `Laura and I are proud of you. Our family is proud of you, but most importantly, America is proud of you. We're excited for you," Johndroe said.
Bush was in Beijing, cheering from the stands, when Phelps claimed his first gold medal by smashing his own world record in the 400-meter individual medley. Afterward, the president and his father, George H.W. Bush, the 41st president, posed for a photograph with Phelps' mother.
"Give your mom a big hug for me," Bush told Phelps on the phone. "Forty-one and I were honored to get a picture with her."