Brown said he was quitting to return to his studies. He is hoping to study for a master's degree at either the London School of Economics or Cambridge University.
"It was an emotional decision to make, but an exciting one for me," Brown said.
"The opportunity to continue my studies at either of those places is fantastic. It was tough making the decision to leave what has been a dream job but I believe it is the right time for me, having just turned 31.
"I told the boys and management team at dinner while we were in Melbourne recently and I'm so glad I did.
"It was good to share it with a bunch of guys who are all real friends as well as team-mates. I thought it would be easy to do till I stood up. It was quite an emotional moment."
Brown's announcement was all the more surprising in that the All Whites will soon begin their qualifying campaign for the 2014 World Cup finals in Brazil.
Having missed out getting on the field during the World Cup finals in South Africa, after suffering a shoulder injury against Australia in a lead-up game, it must have been tempting for Brown to continue.
"The New Zealand team is different to the Phoenix but special in its own way," Brown said.
"It is probably one of the most talented New Zealand sides that I can remember. It is a hugely exciting group.
"But when you embark on a journey like that [World Cup qualifying campaign], you have to give it everything. That's what we did last time and we were rewarded.
"You can't be half-hearted and if you are starting to think about other things, as I was, I couldn't be certain I could give 100%."
The Phoenix plays Sydney in the first round of the playoffs on Friday night.
