Phil Sigsworth made his first grade debut for Newtown Jets in 1977, enjoying a stellar season in 1981 when he made his Test and State of Origin debut while helping take the Jets to the grand final, which they lost 20–11 to Parramatta.
He was selected for the New South Wales Blues for three State of Origin games from 1981 to 1983 and two Tests with the Australian Kangaroos in 1981, he also played in two Interstate Series games that year as well.
The utility back moved to Manly-Warringah Sea Eagles in 1983, where he was judged the Rugby League Week player of the year and runner up in the Dally M Medal as well as scoring his team's sole try in their Grand Final loss that season, again to the Eels. After two seasons with the Sea Eagles he joined the then-premiers Canterbury-Bankstown Bulldogs in 1985. His time at Belmore is remembered for his send-off in the 1986 grand final for a high tackle on Brett Kenny. He is the last player to have been sent off in a rugby league grand final. The Bulldogs suffered a 4–2 defeat to the Eels.
Sigsworth has the distinction of being the only Australian player to participate in three grand finals for three different teams, losing all three matches against the same team (the Eels) but was a member of the victorious Canterbury-Bankstown Bulldogs team in 1985 which was against the St George Dragons.
Sigsworth spent one season with Balmain Tigers in 1987 before drawing the curtain on his Sydney first-grade career because of an in-operable knee injury.