No doubt, people winning olympia medals are amazing physical specimins. no doubt they out-train everyone, they are driven beyond belief, and they live for this stuff. No doubt they've been doing it for their whole lives and would still be world-class athletes without drugs.
However, if you were going to pick out the random guy winning piles of gold medals, and you had to bent the rent check on whether or not his coach might adminsiter test or gh or something for recovery at some point during the year... well, smart money would be on "not natural".
Sure, it's possible that Phelps is all natural. Just not likely. It would make him the most amazing physical specimin ever - surrounded by athletes using drugs. Sure, it's possible. Statistically, not probable. Until they have a hgh test, which they don't have now, these guys will have recovery help that is absolutely undetectable. Does Phelps choose to do the right thing and avoid an undetectable drug which can help him recover faster from his 5-hour training regimens? We don't know that.