Phoenix were bottom of the pile with just five points last month but have now put together back-to-back wins that suddenly have them looking up towards the play-off spots.
Despite the scoreline, Phoenix spent much of the game under pressure but prevailed thanks to a fine performance from goalkeeper Oli Sail - whose eight saves earned him the man-of-the-match award - and clinical finishing, with Reno Piscopo opening the scoring with a fierce drive from outside the box in the 30th minute.
David Ball made it 2-0 soon after as he turned in James McGarry's cross and Perth's hopes of a dramatic turnaround were effectively ended just prior to the hour mark, Ben Waine prodding in from close range.
Wellington's next opponent, Western Sydney, secured its own morale-boosting victory a little later as it climbed up to third.
Jordon Mutch's first A-League goal in the 57th minute was the difference, as the English midfielder pounced on a defensive mistake and capitalised emphatically.
United was adamant they should have been awarded a late penalty when Simon Cox appeared to drag Besart Berisha to the floor by his shirt.
But much to the Kosovan's dismay, the decision did not go to a review and Western Sydney held on to end a run of two defeats and a draw in their previous three games.