Phillis is a variant of Phyllis — from the Greek phyllon (leaf, foliage). Phillis Wheatley (c. 1753-1784) — *enslaved African American woman who in 1773 became the first African American author of a published book of poetry — Poems on Various Subjects, Religious and Moral, published in London after Boston publishers refused. Kidnapped from West Africa as a child of about 7, enslaved by John and Susanna Wheatley of Boston who recognized her gifts and taught her to read English, Latin, and Greek; she was reading classical literature within 16 months of her arrival. George Washington wrote her a letter of thanks in 1776 for a poem composed in his honor. Manumitted (freed) on the publication of her book; died in poverty at about 31. Her surviving 145 poems are foundational to African American literature*.
Subject of Vincent Carretta's Phillis Wheatley: Biography of a Genius in Bondage (2011).
Phillis does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Phillis reduce to 4, The Builder. This is a traditional interpretive system, not a factual claim about the name.