A common misconception about Michael Phelps is that he has an abnormally long wingspan, while it is about average for his height. Studies show that a wingspan is on average 2.1 inches longer than your height and Phelps is 6'4 and has a 6'7 wingspan. To compare some other althetes with actually abnormal wingspans

Draymond Green height: 6'7 wingspan 7'1

Kawhi Leonard height: 6'7 wingspan 7'3