Antonyms for the word "more phosphorescent" include "less phosphorescent," "non-phosphorescent," and "dim." These words indicate a lack of brightness, luminescence, or fluorescence that is often associated with phosphorescent materials. Other antonyms could include "unilluminated" or "dull," which further emphasize the absence of light or glow. While phosphorescence is typically associated with radiance and energy, the opposite qualities can also be used to describe materials that do not exhibit this property. Regardless of the context, antonyms for "more phosphorescent" imply a lack of light, energy, or vibrancy.