I really don't understand why Phoebe would confide in Lily anyway. It's not as if Lily is likely to have much relevant experience, and surely Phoebe has other female friends?
2nd cousins once removed, or posdibly 3rd cousins) so close relations...
(Slightly list track of the generationa and can't be bothered to check.)
Lily sort of took over, rather than giving Phoebe a chance to speak, and wasn't listening any time Phoebe tried to say anything much. I think Phoebe probably found it easier to go along with it than argue, on the grounds it would be over sooner that way.