Can anyone post a self-contained reference concerning the extension of the Euler phi function to number rings and its basic properties (reminiscent of those that the classic Euler phi function has)? Such properties have been shown and proved for this function in a few posts here on MathOverflow.
One such post: Generalized Euler Phi Function
This generalized phi function has also appeared in several papers concerning distribution of prime ideals without any reference to its properties. The one reference that I did have was from Ian Kiming's Algebraic Number Theory notes, and the link to this seems to be gone now.