Last weekend, he was the only South African line judge at the Barclays ATP World Tour finals in London.
This time, he was watching cracker serves from the world's two top players, Roger Federer and Rafael Nadal, as a rotating line judge for the final match.
In addition to split-second decision-making in front of 2.9-million TV viewers, Phiri had to contend with Hawk-Eye - a laser camera used to judge the accuracy of line calls.
The result? Phiri 3, tennis pros 0. "I had three challenges to my calls, but all of mine were spot-on," said the eagle-eyed 35-year-old who now lives in Atteridgeville, Pretoria."
He recalled his first sight of the game: "The first time I saw a tennis court was at some houses in Dennilton. I was unable to enter that place. I used to pass there and watch."
His tennis career started with the gift of a racket from his sister. "I was nagging her to buy me one. When I started, I was already 21. I would say I had a good serve, not as accurate as Roger (Federer), but I would bang in a couple of aces."
When he realised he was not destined to win on the court, he signed up for an officiating course. Recruited into the north Gauteng officiating programme of the SA Tennis Association (Sata), he proved his worth and umpired at smaller events.
He passed a chair-umpiring course and received his white badge certification from the International Tennis Federation, allowing him to work at bigger local tournaments.
His big break came at this year's SA Tennis Open when he was invited to work at the London tournament as part of an ATP international outreach umpiring programme.
"When we broke the news to him, he couldn't believe it. He was very emotional," said Iain Smith, Sata manager of officiating and junior tennis.
"It just shows that it doesn't matter what your background is. If you've got talent and you are good, then it is up to the individual to decide where he wants to go, because the opportunities are now starting to come."
Smith said Phiri's perfect umpiring scorecard had also bolstered the reputation of SA officials. "If you look at what they are achieving with such little exposure (to top international tournaments), it is remarkable."
For Phiri, Sunday's final was business as usual, and not even the sight of Federer and Nadal striding across the court could break his concentration. "There is a wow moment when you first see them, and then you are just an official. You need 110% concentration. If you lose focus, you will not be able to see where the ball bounces. You need to focus on your line so you can't watch the match too much," he said.