The former Ireland head coach, 53, had endured a difficult time since taking charge in April last year.
A year ago, he was suspended and then reinstated following comments he made about team selection.
Joel Garner, Henderson Springer and Roddy Estwick will lead the team when they face Pakistan in three T20s, three ODIs and three Tests in the UAE.
The first match - a T20 game - takes place on 23 September in Dubai.
The West Indies Cricket Board (WICB) cited "differences in culture and strategic approach" with Simmons.
The former all-rounder had questioned the omission of all-rounders Dwayne Bravo and Kieron Pollard from the one-day squad last year.
He was suspended by the WICB, who said Simmons had appeared to "question the legitimacy of the selection process".
The departure of Simmons follows the sacking of Curtly Ambrose as bowling coach and Darren Sammy as T20 captain.
West Indies are currently third in the world T20 rankings but lie eighth in both Tests and one-day internationals respectively.
Phil Simmons has been sacked as West Indies coach just five months after their stunning World T20 triumph.