He made his Wallaby debut in 1989. He enjoyed a rivalry on the pitch with New Zealand's Sean Fitzpatrick. During one Bledisloe Cup match he scored a try by barging through Fitzpatrick and then made a two fingered gesture to him and saying something which most TV watchers thought they could lip read. Kearns insisted he said "Two sausages at tonight's barbecue please". The catalyst for this incident was from the previous season when Fitzpatrick sledged Kearns without mercy, telling him to "Go home to your Mummy". He was a member of Australia's Rugby World Cup-winning teams of 1991 and 1999. Although he was injured mid-way through the 1999 tournament he is one of only six players to be twice involved in a World Cup-winning side. Retired since 1999, he now commentates on rugby for the Fox Sports TV channel.
In October 2005, Phil Kearns accidentally ran over his 19-month-old daughter, Andie, in the driveway of his home. After a long hospital stay, his daughter made a full recovery. Phil Kearns later launched a driveway safety campaign.
Kearns is the brain behind the Sydney Charity Event, The Balmoral Burn. An annual run up one of Sydney’s steepest streets.