Phoebe Eudokia Black (1810-1882) was the eldest daughter of Nigellus Black with Eudokia Carlock as well as their second child. She is also the third child and second daughter of Nigellus Black, the younger half-sister of Alexia Walken Black, the younger sister of Licorus Black and the elder sister of Hesper Black and Eduardus Black.
Phoebe was Nigellus' plain Jane daughter. She went to Hogwarts in 1821 and was sorted into Slytherin House. She was a prefect and a Head Girl. She got nine N.E.W.T's and was greatly gifted at astronomy.
She never married or had any children but worked as an astronomist untill 1844, when she wrote her first book on astronomy. This was followed by a sequel in 1849 and a trequel in 1853.
In 1853, during a book session, she was asked about her supposed/suspected half-sister in America Alexia Walken Black and Phoebe answered:
"This Alexia is a child of my father Mr. Black, yes, but she is illigitimate. Me and my siblings, my real pure-blooded siblings that is, met her once or twice but we have no real relationship with her or her Muggle mother, I can assure you."
- She claimed Alexia's mother is a muggle but Dalassena Walken was actually half-blood.