In response to the above post by @twoleftears, let me say that Spector didn’t have a deep enough education in music theory and composition to have alone created his 1960’s recordings, with their relatively-sophisticated horn and string arrangements. It was Jack Nitzsche who wrote and arranged all those parts for Phil.
Jack Nitzsche later did the same for Buffalo Springfield, Neil Young (he’s the pianist on Neil’s Harvest album), The Stones, Randy Newman, The Tubes, Tim Buckley, and produced albums for Crazy Horse (their fantastic debut album), Mink DeVille, and Graham Parker. He also did some fine film soundtracks (One Flew Over The Cuckoo’s Nest, Performance, The Exorcist), and in 1972 did a very interesting album entitled St. Giles Cripplegate, a modern Classical composition that was performed by The London Symphony Orchestra conducted by David Measham. The album was issued on LP by The Initial Recording Company (catalog no. IRC 006) in England, and by Reprise Records in the U.S.A. (MS 2092).