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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."
Watch the full interview with Didier Drogba in The Premier League show on BBC Two on Thursday, 13 April (22:00 BST) .

Ministers and other government officials are being given a three-month deadline to hand over state-owned homes and vehicles, from the date of the new president's inauguration.
The law targets presidential appointees who try to cling on to the perks of office after a new leader is elected.
Ghana goes to the polls on 7 December.
After previous transfers of power, some officials have had to be forcibly evicted and had their state-owned vehicles seized after failing to hand them back.
The law does not apply to presidents and vice-presidents as we earlier reported.
The bill, which was passed by MPs on Wednesday evening, will now go to the president to sign into law.
Existing legislation requires officials to hand back government property after they leave office, but this is the first time a strict time limit has been applied.
Ghana's current leader John Mahama is standing for re-election and his main opponent is Nana Akufo-Addo. The winner will be inaugurated on 7 January 2017.
Ghana's presidential candidates:

The former HSBC bank building on the corner of Bute Street and James Street is due to house 16 flats including a four-bedroom penthouse apartment.
Cardiff planners said the proposals would help regenerate the area.
The Victorian Society opposed the plan, saying it "would cause a high degree of unjustified harm" to the building.
The four-storey building was constructed in 1874 for coal owners and exporters Cory Bros and was altered and extended in 1914.
The building has been empty since 2014 and planners, in their report recommending approval to councillors, said the proposals were "welcomed in principle as the development would revitalise a large long-term vacant listed building".
They said the changes to the roof showed "appropriate regard to the special interest of the building".
But The Victorian Society had objected to the plans - particularly the penthouse - saying it would "cause a high degree of unjustified harm to the listed building and surrounding Mount Stuart Square Conservation Area".
It said the building "proudly and splendidly evokes the extraordinary wealth Cardiff enjoyed at the end of the 19th Century".
Cardiff council's planning committee passed the proposals on Wednesday subject to conditions and the development starting within 18 months.
Former Chelsea and Ivory Coast striker Didier Drogba has joined United Soccer League side Phoenix Rising as a player and co-owner.
[NEXT_CONCEPT]
Outgoing ministers in Ghana could be forcibly evicted from their official residences if they fail to move out in time, under new laws.
[NEXT_CONCEPT]
Plans to turn a Grade II-listed building in Cardiff Bay into a restaurant and flats have been given the go-ahead by the council.