They called her Phillis because that was the ship name that brought her and Wheatley, which was the name of the merchant who bought her.
She was born in Senegal. In Boston, slave traders put her up for sale:

-She's seven years old! She will be a good mare!

She was touched, exposed, by many hands.

At thirteen, she was already writing poems in a language that was not her own. No one believed she was the author. At twenty, Phillis was questioned by a court of eighteen illuminated men in gown and wig.
She had to recite texts from Virgil and Milton and some messages from the Bible; and also had to swear that the poems she had written were not plagiarism. From a chair, she took her interminable test until the court accepted her: she was a woman, black, enslaved, but she was a poet.
Phillis Wheatley was the first Afro-American writer to publish a book in the United States.