But back then Schooling was just one of thousands of kids queuing to get a picture with the world's greatest swimmer.
Fast-forward eight years and Phelps is now well aware of who Schooling is.
The young swimmer carved out his own little bit of history yesterday by becoming the first Singaporean man to reach an Olympic swimming final.
He finished with a time of 50.83sec in the second 100m butterfly semi-final of the night - a new national record and the world's best time so far this year. In doing so, Schooling was faster than a qualifying pack that includes Phelps, who has already won four gold medals in Rio.
Phelps has 22 of those in total, including three in the 100m butterfly from the past three Games.
Schooling admits he has studied video of Phelps for years to help him improve.
But he told an ESPN documentary in 2012 that he was keen to chart his own career.
"I don't think I've ever daydreamed about Michael Phelps' career - but as far as his accomplishments go, I think everyone would love to have 14 gold medals at the Olympics, and I think over 20 golds at the world championships," he said.
"I just want to make my own career for myself. Michael Phelps may be my idol, but I just want to make my own career."
In 2011, Schooling beat Phelps' age-group (15-16 years) time over the 100 yards butterfly (short course). Beating markers laid down by his idol had long been an obsession, he said. "It's been a target of mine and I'm really happy to do that. It is a huge boost.
"Hopefully, I can get more of his records."
The next year, they raced alongside each other in the United States in what Schooling said was "a tick off on my bucket list". That was followed by a handshake.
Then at the London Olympics that year, Phelps comforted Schooling after their 200m butterfly heats.
Less than 10 minutes before the race, Schooling's equipment was deemed to not fit Olympic regulations, and the then 17-year-old clocked a poor timing.
Schooling said: "I was walking behind Phelps after my race when he looked at me and asked, 'what's wrong?'
"I told him what happened and he hugged me and said, 'you're only so young, you still have a long way to go. It's a learning experience so keep your head high and just keep moving on'."
Schooling had said after an early race with Phelps: "I know that as I get older, I'll become stronger, and I'll fare better beside him."
Yesterday, Phelps was seen giving Schooling a congratulatory tap after they faced off, side by side, in the 100m butterfly heats, which Schooling won.
