Back in 1964, the Rolling Stones were young and new to the music scene. They appreciated music more than they appreciated money and were naive to the financial power they would possess if they unleashed their talented songwriting ability. Which, of course, they did. But along with youth comes ignorance to the legalities of songwriting when it comes to crediting. If Mick Jagger and Keith Richards had the knowledge and experience they have now back then, you can guarantee that all early self-written Stones tracks would be credited to Jagger/Richards. But the controversy regarding Mick and Keith's selfishness when it comes to crediting other people in writing songs is another story. After all, it is one of the reasons Mick Taylor left the band in December 1974.
But the idea of crediting songs to a conceptual, intangible person came from Brian Jones in October-November 1963 after the track "Stoned" was recorded. When the Stones decided to release "I Wanna Be Your Man", a Lennon/McCartney song, they selected "Stoned" to be released as its B-side (although it was misprinted as "Stones" on the original sleeve). Because the song practically has no lyrics, and since it is more of a studio jam than a song itself, Brian suggested that they credit the song to "Nanker/Phelge". According to Bill Wyman's 2002 book, Rolling with the Stones, the word "Nanker" originated from a "revolting face that band members, Brian in particular, would pull" and the word "Phelge" from "Edith Grove flatmate Jimmy Phelge".
In this sense, Nanker Phelge (or Nanker/Phelge) was a pseudonym for the collaboration of Mick Jagger, Keith Richards, Brian Jones, Charlie Watts, Bill Wyman, and sometimes even pianist Ian Stewart, as credited in the ASCAP database. When songs were credited to Nanker Phelge, the whole band would share writing royalties.
Songs credited to Nanker Phelge include "Stoned", "Little by Little", "Andrew's Blues", "And Mr Spector And Mr Pitney Came Too", "Now I've Got a Witness", "Stewed and Keefed (Brian's Blues)", "2120 South Michigan Avenue", "Empty Heart", "Off The Hook" (now credited to Jagger/Richards), "Play with Fire", "The Under Assistant West Coast Promotion Man", "The Spider And The Fly" (now credited to Jagger/Richards), "I'm All Right", "Aftermath", "Godzi", and "We Want The Stones" (recording of live audience cheering for the Stones).
So, you may have noticed that a couple of track's writing credits have changed to Jagger/Richards over the years. Is this due to Keith and Mick taking advantage of the absence of Brian Jones, Bill Wyman and Ian Stewart and the reservedness of Charlie Watts to gain more writing royalties? Or is it just the fact that time has evolved from Nanker Phelge and it has been forgotten? Perhaps both are true, the latter especially - try searching Nanker Phelge in the American Society of Composers, Authors and Publishers (ASCAP) online database; you will be redirected to songs written by Mick Jagger and Keith Richards. It is even rumoured that "Paint It, Black" was originally credited to Nanker Phelge but changed to Jagger/Richards by mistake.
After the use of "Nanker Phelge" for songwriting credits was obsolete, the name re-emerged on the original sleeves of the albums Beggars Banquet (1968) and Let It Bleed (1969) as responsible for manufacturing. As Keith Richards describes in his autobiography, Life, the members of the band all shared in a company in the UK called Nanker Phelge Music. After signing a deal in New York which would channel all their material through another company called Nanker Phelge USA, and assuming that it was the same company but with an American name, the Stones soon realised that then co-manager Allen Klein owned the American version in its entirety. This led to a legal battle that would stretch over seventeen years. A settlement was reached such that Klein (now deceased) owned the copyright of all of the Rolling Stones' work up until 1971, and his estate still retains publishing rights.