Paul McCartney on Brian Jones (1969):
“I liked Brian. We asked him to one of our sessions and to our surprise he brought along a sax. He turned up in this big Afghan coat at Abbey Road. We said, ‘We’ve got a little track here’, and he played sax. It was a crazy record, ‘You Know My Name, Look Up the Number‘. It’s a funny sax solo, exactly what we wanted, a ropey sax, kind of shaky, Brian was very good like that.”

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From Beatles Fandom:
The song is a music hall comedy number and is perhaps the silliest song in the Beatles’ catalogue. Lennon came up with the lyrics and title after seeing a phone book.

McCartney once told Beatles recording analyst Mark Lewisohn, “[People] are only just discovering things like ‘You Know My Name (Look Up the Number)’ — probably my favourite Beatles’ track!”
The song features a saxophone solo played by the Rolling Stones’ Brian Jones.

The song moves through several sections which appear to be stylistic references to some of the Beatles’ contemporaries including Mick Jagger of the Rolling Stones, and Trini Lopez. The Trini Lopez or “lounge” section includes a reference to Dennis O’Dell, associate producer on the A Hard Day’s Night film,. Partway through the song, Lennon introduces McCartney as lounge singer “Dennis O’Bell,” one consonant away from the name of the film producer Lennon had worked with not only on A Hard Day’s Night but also How I Won the War. The reference prompted numerous telephone calls to O’Dell’s home by fans who told him, “We have your name and now we’ve got your number,” as well as personal visits by fans wanting to live with him.
(Ref. paul mccartney on brian jones)