The mythical phoenix had red and gold feathers. It lived a long time and, in its old age, built a next that it then started on fire. The old bird was burned up and a new bird reborn in its place.
In "A Worn Path," Phoenix is quite old. She wears a dark dress, but a golden color shines through from her skin, and the second paragraph tells us "and the two knobs of her cheeks were illumined by a yellow burning under the dark" (she burns like a phoenix).
She also is reborn in some ways, or is working to help others be reborn. She was a slave, but is free. Her memory dies, but comes back. She is old, but is buying toys for the young.