Phoenix head coach Darije Kalezić said the signing represented an important addition to his squad.
"He's a pro-active player, he has good quality and a strong winning mentality – he won the championship in Lithuania and produced the most assists in the team. I am confident he will add greatly to our playing group.
"Matija is the product of the best youth academy in Serbia [Partizan Belgrade], one of the best in Europe, so he comes with great technical skill and basis, he will contribute strongly with final passes to create goals."
Ljujić will be available to make his for the match-day squad in Wednesday's clash against the Melbourne Victory in Wellington and was expected to suit up alongside fellow recent signing Nathan Burns.
His addition is the second for the team this week, with Dario Pot confirmed as the team's new assistant coach.
Pot previously worked with Kalezić during his two seasons in charge of De Graafschap in the Netherlands from 2009-11 and has been with the squad for their last two away games.