The Kiwi outfit has described the 26-year-old as one "of the most gifted and talented players to grace the A-League".
Kopczynski made his debut for his boyhood club Legia Warsaw in Poland in 2012 and went on to make 77 appearances, including playing 17 times in last season's title-winning effort.
In 2016-17 he helped The Legionaries qualify for the Champions League, playing in over 30 games - including 11 European matches - and facing off against the likes of Real Madrid, Borussia Dortmund and Sporting Lisbon.
The signing follows the recruitment of Polish compatriot, Filip Kurto, which should help ease the transition.
Phoenix coach Mark Rudan identified a deep lying midfielder as a key priority for the team.
"Michal has all the attributes for what I require in a holding midfielder and those key skills to excel in the A-League," Rudan said.
"He’s got drive, composure, skill, vision, and grit to cover a lot of ground and work hard for the whole team.
"Besides giving everything for the shirt and an incredible attitude to win, he will be the kind of player the fans will love to come and watch.
"Michal’s got all the skills to light up this league."
Kopczynski said talking to Rudan proved the deciding factor in making the switch to Phoenix.
"I wanted to experience something new in playing abroad and talking about the project with Mark helped me to decide to come to Wellington," he said.
"He’s clear about what he wants in his players and what he needs from me. I have heard about Filip (Kurto) signing so it will be good for me to help settle in."