Phil Stewart grew up in Toronto in a musical household. His father was a part-time jazz guitarist who transcribed Charlie Parker, Coleman Hawkins and Wardell Gray solos for his sons, and his older brother, tenor saxophonist Grant Stewart, was playing those transcriptions at ten and leading a quartet in Toronto by eighteen. Grant left for New York at nineteen, in 1990. Phil stayed behind for most of the decade.

His earliest documented recording comes from that Toronto period: Maroon (Village Jazz VJCD-9902), a Ken Skinner big-band date cut on May 27 and 28, 1996, with Stewart on drums, Duncan Hopkins on bass and two alto saxophonists who matter to the rest of his story. One was Bob Mover, the American bebop player then living in Canada who had given Grant Stewart some of his first professional work. The other was Josh Benko, whose tune "The Sumo" Phil Stewart would record twenty-one years later on his own leader debut.

He relocated to New York in 1998. He studied privately there with several of the drummers he had grown up listening to; published accounts of who he worked with vary, but Joe Morello appears in all of them, and Sam Ulano, Vernel Fournier, Jimmy Cobb and Joe Farnsworth are each named in one or more. His working home became Smalls, the basement room on West 10th Street that had already absorbed his brother. The Smalls circle he joined was the one built around pianist Sacha Perry, bassist Ari Roland, alto saxophonist Zaid Nasser and tenor saxophonist Chris Byars, the group of players who had learned the music directly from Frank Hewitt and Barry Harris. Between 2005 and 2008 he recorded seven albums for Luke Kaven's Smalls Records with them: Perry's Eretik (2005), Not Brand X (2006) and The Third Time Around (2007), Roland's Sketches from a Bassist's Album and And So I Lived in Old New York..., and Nasser's Escape from New York (2007) and Off Minor (2008).

The same years brought his long association with pianist and organist Ehud Asherie. Stewart plays drums on four of Asherie's leader dates, spanning seven years and two labels: Lockout (Posi-Tone, recorded February 5, 2007), Asherie's debut, with Grant Stewart, Ryan Kisor and Joel Forbes; the piano trio Swing Set (Posi-Tone, recorded October 26, 2007) with Neal Miner; Organic (Posi-Tone, 2010), built on Hammond organ rather than piano, with Peter Bernstein and Dmitry Baevsky; and Music Makes Me (Gut String, recorded in New York in August 2013), again with Miner. He had already appeared with Asherie on Samba de Gringo, the 2005 duo record Asherie made with the Brazilian singer and guitarist Bina Coquet.

Since 2005 he has been the regular drummer in his brother's bands, a partnership documented across two decades of Grant Stewart records: Tenor and Soul (2005) and Estate (2005) for the Japanese label Videoarts, Plays Jazz Ballads (2009) and St. Thomas: Grant Stewart Plays Sonny Rollins (2010) for Birds, Around the Corner (Sharp Nine, 2010), Live at Smalls (SmallsLIVE, recorded April 6 and 7, 2012), and then a run for Cory Weeds's Vancouver label Cellar Live and Cellar Music: Trio (2015), Roll On (2017), Rise and Shine (2020), The Lighting of the Lamps (2022) and Next Spring, recorded at Van Gelder Studio on November 3, 2024. With that quartet he has played Japan, France, Germany, the Netherlands, Switzerland, Russia and Uruguay.

He made his own leader debut relatively late. Introducing Phil Stewart: Melodious Drum was recorded on July 2, 2017, and issued by Cellar Live in February 2018. The groups run from trio to sextet around a core of Sacha Perry on piano and Paul Sikivie on bass, with Grant Stewart on tenor and alto, Chris Byars on tenor and Joe Magnarelli on trumpet. The program mixes Dizzy Gillespie's "Manteca," Bud Powell's "Dance of the Infidels," Thelonious Monk's "Eronel" and George Coleman's "Apache" with three Perry originals and Byars's "The Doctor Is In." Away from his brother's band he has recorded for SteepleChase with Chris Byars (A Hundred Years from Today, 2019; On the Shoulders of Giants, 2020; Rhythm and Blues of the 20s, 2022), with the Anderson brothers on Gut String, and with the Fat Cat Big Band. He held a weekly late-night residency at Mezzrow with guitarist Pasquale Grasso through 2017 and 2018, and he teaches drums at the Church Street School of Music and Art in Tribeca. The SmallsLIVE archive lists 272 of his appearances at Smalls and Mezzrow between October 2007 and July 2026, including dates under his own name as the Phil Stewart Quartet.

Stewart is a timekeeper first. Reviewing Melodious Drum for All About Jazz, Jack Bowers wrote that the drums "may be congenial but aren't melodious" in the manner of Jeff Hamilton or Ed Thigpen, and that Stewart "simply keeps very good time without excessive frills or flamboyance, while his solos are forceful yet far from song-like." That is close to the brief the Smalls repertory scene asks of a drummer: the aim there is the bebop and hard-bop language as played, not as updated, and the drum chair is measured by whether the horn players can float on it. Jim Merod's liner note for the same album places him "in the line of Max Roach, Art Taylor, Philly Joe Jones and Louis Hayes" and compares his unshowy control to Vernel Fournier's with Ahmad Jamal and Jo Jones's with Count Basie. His teachers point the same way: Morello, Ulano, Fournier and Cobb are all players whose reputations rest on touch and time rather than volume. The fact that Sacha Perry, Ari Roland, Chris Byars, Zaid Nasser and his brother have all used him continuously for twenty years is the strongest available evidence about what he does; that circle is small, conservative about personnel, and has had many drummers to choose from.