There aren't many by Google, to be honest. A lot focusing on his post-retirement career, his philanthropy gets a bunch of hits, and so on, but even if you narrow down a search to "michael phelps ability", only the top five most relate to physical advantages; the second five trail off into a generic biography site, Wikipedia, and a profile on how his ADHD helped his swimming career. The focus on the biological spans a few articles, one dating back as far as 2008. So in terms of a focus on any biological baseline, not much has survived the onslaught of time (and SEO r.e. web search history).
It might be worth focusing on a particular media cycle / rapid publishing of articles, but they're a lot harder to track after the fact. Certainly nothing a random declaration on CFC can prove. It's certainly easier to search for similar articles about Bolt. The second to top result for the same search ("usain bolt ability") is a link where the blurb exposed to Google mentions "gene" specifically. The similar match for Phelps doesn't (most focus on his "wingspan" and general reach; it takes several paragraphs for the top-rated article about Phelps to even mention lactic acid).
Do note that unless you do it from a private window (and even then there are probably things Google biases by language / general location by ISP) that these things will be impacted by however much data Google has built up on your search history and how it pertains to the subject. I certainly don't go investigating this much, but I used to be a swimmer and my Google profile is pretty much omnipresent for me on any device I use, heh.
