A specimen would be the sure way. A number of the bracket-like Phellinus species recorded for Australia may develop that black, cracked upper surface with age (e.g. Phellinus badius, Phellinus rimosus and Phellinus robustus - if you'd like to do some web searching). Each can also show some variation in naked-eye appearance, but the microscopic features are reliable. Phellinus is a genus that is usually easy to recognize in the field- but identifying the species is another matter.