Mo --

"Phoebe, an epithet of Selene" --

one of meanings of Phoebe given in Wikipedia.

Selene one of the names of moon-goddess, along with Cynthia or Artemis. So it is a case of the conventional adjective [meaning 'shining'] being used attributively in place of the actual name (IIRC the technical name for tropes of this kind is antonomasia). Similarly, the masculine form Phoebus sometimes used for Apollo the sun-god. So Phoebe here does mean the moon, rather than being an alternative for Phoebus; the point being that the singer drinks at home in the evening after moonrise, with just one companion, instead of going out to the inn where he has run out of credit.

~M~