The Under Armour video, created by the Droga5 agency, offered a 90-second glimpse of one of the world's most famous athletes working through "his solitude, his pain and his sacrifice away from the spotlight," Adweek said in its list released Sunday.
"It did so with a haunting beauty that wrapped the hardship in romance, illuminating the athlete's love of a sport whose cruelties have also brought fame, fortune and 28 Olympic medals," Adweek said.
The Baltimore-based sports apparel maker had asked Droga5 to show Phelps' perspective on training for his final Olympics. It was part of the brand's "Rule Yourself" campaign, ending with the tag line "It's what you do in the dark that puts you in the light," and set fittingly to "The Last Goodbye."
Adweek called the spot "astonishing, using darkness to paradoxically shed new light on one of the planet's biggest stars -- and the physical and psychological cost of dedicating one's life to swimming."
Droga5 group creative director Tim Gordon told Adweek that "this is someone everyone thought they knew, but in many ways did not."
Phelps told the publication that the video not only showed it like it is but helped motivate him ahead of Rio.
"As long as you're literally busting your butt every single day, you'll see the goal at the end of the road," he told Adweek.
The No. 1 ad in the top ten list beat out the pick for best Super Bowl ad, a 60-second Jeep video showing portraits of Jeep drivers, which ranked 6th, a Christmas ad for H&M starring Adrien Brody, at No. 5, and Nike's 'Da Da Ding,', a 3-minute ad starring women athletes in India, where girls are told "sports is a waste of time," Adweek said.
Though it was picked by Adweek as the best Olympic ad, the spot never mentioned the games by name because Under Armour was not an official sponsor.