The 23-year-old American was then back in the pool for the semi-finals of the men's 100m butterfly, qualifying second fastest for the final in 50:97 despite being in sixth place at the halfway mark.
He fitted the medley medal ceremony in between events, which led to some frantic behind-the-scenes action.
"I didn't know I had as little time as I did," he revealed. "I didn't even have time to go into the ready room. I went directly from the pool deck to taking my award sweats off and putting my parka on, trying to put my cap and goggles on and tying my suit.
"Then they were pushing us out. I had about two minutes to do all that. The only thing I wanted was to win my heat in the 100m fly and get a centre lane for the final."
Phelps competes tomorrow morning in the 100m butterfly final with the chance of equalling Mark Spitz's record in the 1972 Munich Olympics of seven gold medals in a Games.
If he wins, his quest for an unprecedented eight golds begins in the afternoon session in the heats of the 4x100m medley relay with the final on Sunday morning.
Phelps claimed tomorrow's final is the most important for him in Beijing.
He said: "I want to be able to get out of the first 50m a little quicker than I have in the last two races. Yesterday, to be a body length behind in the last 50 wasn't where I wanted to be."
After being close to tears during the ceremony for his fifth gold two days ago, Phelps admitted he kept his emotions in check on the podium today.
"I have to conserve as much physical and emotional energy as I can. I'm down to the last two races and I am going to try to rest and recover as much as I can and prepare myself."
Tancock, who knew he had no chance of winning, paid tribute to Phelps.
He said: "He's doing great things for the sport. It's amazing being in the same era. He is a modern day hero. We've seen it in tennis, golf and F1 and he is doing a great job for the sport. It's the story of the Games."
Another world record fell in the 200m backstroke when Ryan Lochte beat fellow American and defending champion Aaron Peirsol, with whom he shared the previous world record.
Lochte won in 1:53:54 with the Scot Gregor Tait finishing eighth.
In the 200m breaststroke final, another American, Rebecca Soni, beat Australian world record holder Leisel Jones in 2:20:22.
The women's 100m freestyle final was won by German Britta Steffen with Fran Halsall finishing in eighth.
Britain also had two swimmers in the semi-final of the women's 200m backstroke, with Elizabeth Simmonds qualified for tomorrow morning's final as seventh fastest but Gemma Spofforth narrowly missed out in ninth place.
