the little o is the 0 - J> minus phi, o = 0 . In others words it is from this angle that the © (phi) comes to symbolise what is lacking to the 0 in order to be the noetic 0, the 0 in full exercise
Lacan argues that the phallus as object functions precisely to symbolise what is structurally lacking to the Other, making lack a constitutive feature of desire and the subject’s relation to the big Other.
, The Seminar of Jacques Lacan, Book VIII: Transference, 2015thesis