World body Fina let off Sun with a warning, which essentially meant no punishment for what should be an egregious violation of doping rules — especially since the swimmer tested positive in 2014 for a banned substance.
Sun still faces a hearing before the Court of Arbitration for Sport that could lead to major sanctions but the lack of action by a governing body long viewed as laughably inept prompted two swimmers to take a bold stance in Gwangju.
Australia's Mack Horton, a long-time rival of Sun, refused to take a spot on the medal stand after finishing second to him in the 400m freestyle. Britain's Duncan Scott did the same after settling for a bronze medal in the 200m freestyle, also won by Sun.
Phelps, who has said he never felt like he swam a final that didn't include at least one doped-up swimmer, can understand the frustration.
On the other hand, he doubts their dramatic gesture will have any real impact.
"I love how people are standing up and voicing their opinion," he said. "But at the end of the day, there's only one person, only one group of people who can really change this. That's Fina. When Fina wants to do something, wants to change how this sport is seen after all these positive drug tests that are occurring, after all this controversy, maybe they'll do something about it.''
Fina has shown no eagerness to aggressively tackle the doping issue.
In fact, the organisation hastily added rules to its code of conduct designed to stifle the sort of silent protests made by Horton and Scott.
While encouraged by the efforts to form a swimmers' union, which would give the athletes a greater say in the way the sport is run, Phelps isn't so keen on individual protests like the ones seen in Gwangju.
"When your energy goes into that, it takes away from your swimming," Phelps said. "I was very clear how frustrated I was that people chose to use performance-enhancing drugs instead of preparing themselves, putting in the work and putting in the training and doing what it takes to be a champion instead of taking the easy way out. But I wasn't going to waste my time and my energy to focus on somebody else and what they were doing. That was out of my control."
That approach worked well for Phelps. He won 23 Olympic golds, and 28 medals overall, before retiring after the 2016 Rio Games. At 34, he is content with his staggering legacy and laughs off any suggestion that he might launch another comeback.
But swimming will always be a huge part of his life.
He still heads to the pool almost every day, recognising it's as much a mental salve as a means of staying in shape.
"That's the one place where I can clear my head," said Phelps, who battled depression during his career. "It's so quiet in the pool."
He is still involved in the business side of the sport, running the MP swimwear line with an eye towards building "my own little dream team" for the Tokyo Olympics.
As for the seedier side of swimming, Phelps will continue to speak out. He supports a one-and-done philosophy for dopers, believing anyone who tests positive should automatically receive a lifetime ban.
He'll keep pushing those in charge to do the right thing, while remaining realistic about the prospects for any significant change.
- AP
