Drogba, 39, has not played since leaving Major League Soccer club Montreal Impact in November.
He will start out as a player but has also joined Phoenix’s “MLS expansion franchise ownership group”.
“To own a team and be a player at the same time is unusual but it’s going to be very exciting,” Drogba said.
“It’s a good transition because I want to carry on playing but I’m almost 40 and it’s important for me to prepare for my later career.”
Phoenix have just started their fourth season in the Western Conference of USL, which forms part of the second tier of the American league system.
The Arizona club hope to become one of four planned expansion teams in MLS over the next three years.
“I had offers from China, from England – in both the Premier League and even the Championship – but they were only as a player,” Drogba told The Premier League Show.
“This was the right offer because it was important for me to think about playing, because I enjoy it, but also to get to the next stage of my career.”
Drogba scored 157 goals in 341 appearances during his first spell at Chelsea from 2004 to 2012, winning three Premier League titles and the Champions League.
Following moves to Shanghai Shenhua in China and Turkish side Galatasaray, Drogba returned to the Blues for the 2014-15 season, scoring seven goals in 40 appearances, helping Jose Mourinho’s side to the title, before 18 months with Montreal.
He joins former Chelsea team-mate Shaun Wright-Phillips at Phoenix, who have one win and two defeats from three games this season.
“I’m still a player but it’s important to respect the decision of the manager,” added Drogba, who is Ivory Coast’s record goalscorer.
“When we’re on the pitch, he’s going to be the one who decides and when we go to board meetings, it’s a different thing.”