Abbas, 30, joins the Phoenix on a two-year contract.
The Iraqi international has been a free agent since leaving Korean outfit Pohang Steelers at the start of the year. 
Abbas, a former Newcastle Jet and Sydney FC player, is now back in the A-League for his third stint in the competition. 
“After Korea there were many offers, a lot from home in Iraq, but I wanted to come back to the A-League,” Abbas said.
“Phoenix have many quality players, they’ve recruited well – I want to do something special this year.
“At Sydney I worked with [Phoenix assisant coach] Rado[Vidosic], he’s very tactical, and structured, he makes you understand the roles you play, so the chance to work again with him, and of course to learn from [Phoenix head coach] Darije [Kalezic], was very exciting.”
Vidosic added: “Ali provides us with a lot of experience from the A-League, Asian Champion’s League and overseas.
"As a left-footed player he also brings a lot of balance to the team and also competition on the left-handed side – at fullback, as a midfielder and a winger."
Abbas joins Dario Vidosic, Goran Paracki, Daniel Mullen, Scott Galloway and Andrija Kaludjerovic as off-season signings. 
However, Abbas is only initially signed as an injury replacement for Louis Fenton.