Phil Miller was a self-taught musician and began playing the guitar at age 15 under the influence of the great blues guitarists of the 1950s, but during the 1960s discovered rock and jazz, which he integrated into his playing. Miller was educated at Lexton School (near Corby), then Cambridge Technical College.
Miller's first band, Delivery was formed in 1966, when he was 17 with his brother Steve on piano, Pip Pyle on drums, and Jack Monck on bass. Later on, they were joined by Lol Coxhill, and Monck was replaced by Roy Babbington in 1969. With singer Carol Grimes, Delivery recorded the album Fool's Meeting in 1970 which included the first compositions of Phil Miller. In late 1970, Delivery split.
The Miller brothers then joined Lol Coxhill in a new project with vocalist Judy Dyble, which they called DC & The MBs (for "Dyble, Coxhill and the Miller Brothers"), but the project ended when Steve Miller left to join Caravan and, shortly thereafter, Phil was asked by Robert Wyatt to take part in Matching Mole, which recorded two mostly-instrumental records before calling it quits.
Delivery was then briefly resurrected, gradually shuffling its personnel until it turned into Hatfield And The North in 1972. After an extended settling-in period, Hatfield finally got to work recording, with Miller providing looser, more improvisation-based pieces to counterpoint the group's more rigidly structured material. The band only completed 2 records itself before splitting in 1975. The guitarist then moved on with fellow Hatfield players Dave Stewart and Pip Pyle to create the band National Health, an outline of which had been suggested when Hatfield had merged with the band Gilgamesh (2) for two performances in 1973. National Health released two records before disbanding in 1980. A brief reunion of the band took place in 1981 to record a tribute to keyboardist Alan Gowen after his death that same year.
In 1982, Phil Miller founded the band In Cahoots, which was to be his primary musical outlet. Both in-and-out of In Cahoots, Miller continued to collaborate with many of his ex-Hatfield and the North/National Health bandmates, and also toured as a duo with guitarist and bassist Fred T. Baker.