iTunes and iPhone disagree on memory usage

There is a large discrepancy between the memory usage as reported by my iPhone and that as reported by iTunes - as well as between iTunes' Settings pages for the iPhone and the iTunes memory bar at the bottom of the screen. iTunes reports that the iPhone is set to sync my entire music library,

but also claims that only about one third of my songs are actually stored on the phone.

(I'm old fashioned; I still buy and rip my own CDs, and I don't use any cloud services.) Furthermore the phone itself reports that the amount of memory being used for music is three times as much as shown in iTunes.

(I don't know how to get the phone to show a count of songs.) Does anyone know what I need to do to get these numbers to agree?