The former world number one said she hoped to motivate young girls into sports with the doll.
The American smashed Ian Thorpe's 200 metres freestyle world record at the world championships.
Ariarne Titmus and Elijah Winnington led podium sweeps as Australia got the Commonwealth Games swimming competition off to an explosive start on Friday, scooping 11 medals in total including five golds
Katie Ledecky claimed a stunning gold in the women's 200 metres and also won the 1,500m freestyle gold with a world record.
Multiple world champion Pellegrini tests positive for COVID-19.
At 19, Milak is the youngest winner of the 200 butterfly since Phelps triumphed as an 18-year-old in 2003, the second of the American great's five world titles in the event.
Britain's James Guy held off a host of Olympic champions to win his first world title, the men's 200m freestyle, at the world championships on Tuesday.