A season-high crowd of 13,601 at the Westpac Stadium saw the Phoenix rise up to second behind Central Coast.
Ifill opened the scoring but Alex Terra levelled the scores before half-time.
Chris Greenacre's header early in the second half put the Phoenix back in front and Ifill's second in the 64th minute completed the victory.
Perth Glory lie fourth in the table after Shane Smeltz, Steve McGarry and Liam Miller scored in the 3-0 win away to Adelaide United.
Defeat left the home side in the bottom two.