I'd like to note that Wheatley has come under lots of criticism for falling into the white-washed and westernization/christianization that Black people were forced into in order to fit in/be humanized/deemed valuable.
See Cornelius Eady's poem "Diabolic" as a response to Phillis Wheatley's poem "On being brought from AFRICA to AMERICA" where she makes a remark on black peoples skin color being "diabolic." Wheatley's remark is as follows:
Some view our sable race with scornful eye,
"Their colour is a diabolic die.”
Remember, Christians, Negros, black as Cain,
May be refin’d, and join th’ angelic train.
I seems to some, including Cornelius Eady, that Wheatley is suggesting that Black people are inherently evil because of their skin color and that the only way to be redeemed/saved is to be converted into the white people's religion, ie Christianity. Wheatley was deeply religious since her white owners brought her up as such, and perhaps this influenced her and her poetry a lot.
For a more analytical perspective see James Edward Ford III's “The Difficult Miracle: Reading Phillis Wheatley against the Master’s Discourse."