Waking up in the dark can feel lonely, but here it turns into something tender. The poem is a single sentence, and it moves the way a glance does: a woman opens her eyes for just a moment, and the first thing she meets is the moon, bright against the gloom and smiling down at her.
The moon is the real surprise. Instead of a cold, distant object, it becomes a presence that notices her and welcomes her. The poem never says how she feels, but the word "smiled" suggests comfort, maybe even a sense of being watched over. The darkness is only "an instant," so it doesn't feel threatening. It simply sets up the contrast that makes the light seem warmer.
The title, "Phases," may hint at the moon's changing shapes, or at the changing states of waking and sleeping, or of a person's life. The poem doesn't spell it out. What it leaves us with is a quiet, hushed, gently hopeful mood.