After his father’s death, he started playing pop and rock and found work in a production of the musical Jesus Christ Superstar.
He worked as a session musician for cast members, and this led to other session work.
Phillips was the drummer in the Phil Manzanera and Brian Eno supergroup 801 on their 1976 album 801 Live. He replaced Judas Priest drummer Alan Moore on the band’s Sin After Sin album (1977) and went on to record Michael Schenker‘s 1980 debut album The Michael Schenker Group, as well as in Mike Rutherford‘s Smallcreep’s Day. In the early 1980s, Phillips formed part of RMS with session musicians Mo Foster and Ray Russell. He was the drummer for The Who on their 1989 American reunion tour and appeared on solo recordings by band members Roger Daltrey and Pete Townshend.
Around 1978, British guitarist Gary Boyle made an album called „The Dancer“ featuring Simon Phillips. Phillips later also played on Evita where he contributed some fabulous grooves.
In 1989 he recorded his debut album with the band Protocol.
Wanting to make bigger changes in his music career, Phillips decided to move to Los Angeles in the 1990s.
In 1992, Phillips had recently completed the recording of an album in England when he was invited by Toto to fill in for Jeff Porcaro after the latter died following the completion of the recording of Kingdom of Desire.
He became the band’s only choice as Porcaro liked his style and that he toured with Steve Lukather and Carlos Santana on their solo tours. Phillips decided to settle permanently in Los Angeles on that matter and began rehearsals with the band. After the Kingdom of Desire tour, Phillips officially joined Toto.
As the band began its 1995 Tambu tour, Phillips suffered from back problems and was unable to play on the first leg of the said tour; the band turned to Gregg Bissonette to substitute for him. When Phillips fell ill prior to the 2004 Night of the Proms concert, Bissonette was unavailable to take over his drumming duties, causing the band to invite Ricky Lawson instead.
Phillips’ last show with Toto was in 2013. He left the following year to focus on his solo career and was replaced by Keith Carlock.
Five years later he led a band that performed at the North Sea Jazz Festival.
In 2002 he recorded a jazz album, Vantage Point, with trumpeter Walt Fowler, saxophonist Brandon Fields, and pianist Jeff Babko.
After leaving Toto, he became a member of a trio with Hiromi Uehara and bassist Anthony Jackson. Phillips has also worked with Big Country, Jack Bruce, David Gilmour, Big Jim Sullivan, and Whitesnake.
In 2009, Phillips joined with keyboardist Philippe Saisse and bassist Pino Palladino in forming an instrumental jazz/funk rock trio: Phillips Saisse Palladino, PSP, which toured in Europe in 2009 and 2010. Phillips also performed on Joe Satriani‘s album Super Colossal, appearing on multiple tracks. Phillips appears in Alan Parsons‘ Art & Science of Sound Recording educational video series, as well as the program’s single „All Our Yesterdays“. He played in the Michael Schenker Group album In the Midst of Beauty and took part to the band’s 30th Anniversary world tour in 2010. Phillips is featured on Hiromi Uehara‘s 2011 album, Voice. He also toured with Hiromi and bassist Anthony Jackson as part of the Hiromi Trio Project.