I'd personally avoid another 'ee' sounding ending.I love the suggestion of Phoebe and Lydia.
Other suggestions:-
Phoebe and Charlotte
Phoebe and Iris
Phoebe and Ava
Phoebe and Alice
Phoebe and Amelia
Phoebe and Isabelle
Phoebe and Isla
Phoebe and Eliza
Phoebe and Eloise
Phoebe and Violet
Phoebe and Jasmine
Phoebe and Mabel
Phoebe and Olivia
Phoebe and Sophia
Phoebe and Matilda