The 17-year-old, who won the 100m and 200m backstroke titles, has also branded Phelps "the most decorated Olympian of all time".
"Getting to know Michael, to cheer for him, to watch him and see him become the most decorated Olympian of all time has been awesome," she told Sky Sports News.
"It is so inspiring for me and gives me so much motivation. I don't think his shoes will ever be filled. I think his footsteps are huge, but maybe I can make little paths of my own next to his."
Phelps ended his career in London with 18 Olympic golds.