Phillis is a variant of Phyllis — from the Greek phyllon (leaf, foliage). Phillis Wheatley (c. 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. Her surviving 145 poems are to African American literature.
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.