Although it did not parallel the commercial success of the band's previous album, Things Fall Apart, the album reached number 28 on the US Billboard 200 chart and sold steadily, remaining on the chart for 38 weeks. On June 3, 2003, it was certified gold by the Recording Industry Association of America, for shipments of 500,000 copies in the United States. Upon its release, Phrenology received universal acclaim from music critics, who praised its musical direction and lyrical themes, and it was included in numerous publications' year-end lists of the year's best albums.
Following the breakthrough success of Things Fall Apart (1999), its release was highly anticipated and delayed, as recording took two years. The album is named after the discredited pseudoscience of phrenology, the study of head shapes to determine intelligence and character, which was used to rationalize racism during the 19th century in the United States. Its cover art was created by artist/printmaker Tom Huck.
On "Something in the Way of Things (In Town)", Amiri Baraka performs a poem about how the spirit of death and decay permeates African-American urban experiences. Set to a fusion of several African-American music influences, his poem observes "something in the way of our selves" and uses unusual imagery such as death "riding on top of the car peering through the windshield" and a "Negro squinting at us through the cage" with a smile "that ain't a smile but teeth flying against our necks".
Phrenology received universal acclaim from music critics. At Metacritic, which assigns a normalized rating out of 100 to reviews from mainstream critics, the album received an average score of 87, based on 23 reviews.Mojo hailed it as a "masterpiece", and Dave Heaton of PopMatters called it "an impressive, ambitious work". Heaton commended the Roots for "filling their sound out and pushing it in a variety of directions", with a form of "tight soul/funk" that "sounds even more exact, funkier and edgier" than on Things Fall Apart.Chicago Sun-Times writer Jim DeRogatis gave it four out of four stars and called it "a near-classic right out of the gate, an urgent, raucous and thought-provoking 70 minutes that mine the musical territory between hard hip-hop and smoother Philly soul".Blender's RJ Smith called it "a celebration of self-determination, a nonstop joyride through some very complicated brains".Alexis Petridis, writing in The Guardian, found the Roots "exclusively capable of absorbing other genres", while the "more straightforward hip-hop" is "idiosyncratic and hugely enjoyable".Slant Magazine's Sal Cinquemani called the album "subtly progressive" and said that the lyrics "challenge the commodification and subsequent destruction of hip-hop culture".Rolling Stone writer Pat Blashill observed "a startling array of hip-hop reinventions".
Allmusic editor Steve Huey said that the album is "a challenging, hugely ambitious opus that's by turns brilliant and bewildering, as it strains to push the very sound of hip-hop into the future." He also called it the band's "hardest-hitting" album because they successfully "re-create their concert punch in the studio."Robert Christgau of The Village Voice gave Phrenology an "A-", indicating "the kind of garden-variety good record that is the great luxury of musical micromarketing and overproduction". Christgau complimented Kamal Gray's "keyb hooks" and stated "[B]elieve that after years of racial mythology, they've found it in their talent to put black music's long tradition of tune and structure into practice".The Rolling Stone Album Guide (2004) gave it four-and-a-half stars and cited "Water" as a highlight, "that begins with the age-old Bo Diddley beat and ends as an extended musique concrète-style instrumental fantasia".