No you don't need a visa if you got Australian passport. After luggage collection, exit, turn right and at the end of the terminal use the escalators or lifts up to departures.
Be aware that the immigration queue (T3) at check in is usually a 90 minute zoo in the afternoon/evenings. No one cares about foreign/Philippine passport queues and it takes ages to get through.
If short of time go right and check with staff if you can go through the diplomat/aircrew immigration lane instead. It is as far to the right as it gets (I always ask and so far I haven't been denied - helps to dress professional)...
Remember, you must do the online e-travel declaration. It takes 5 minutes but you need it to check in and immigration has it in their system. Since your not filippino you don't need to do it to depart Philippines.
if you have a full day, take the walkway across the road to Belmont hotel. They offer rooms at a reasonable rates and you can sleep a few hours, hit the pool or bar/restaurant.