phase has 3 distinct synonyms spread across 3 of its 6 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
any distinct time period in a sequence of events
“we are in a transitional stage in which many former ideas must be revised or rejected”
Synonyms, antonyms and the broader and narrower relations for phase come from Princeton University’s WordNet. Full sources and licences.
(physical chemistry) a distinct state of matter in a system; matter that is identical in chemical composition and physical state and separated from other material by the phase boundary
“the reaction occurs in the liquid phase of the system”
a particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle
(astronomy) the particular appearance of a body's state of illumination (especially one of the recurring shapes of the part of Earth's moon that is illuminated by the sun)
“the full phase of the moon”
arrange in phases or stages
“phase a withdrawal”
adjust so as to be in a synchronized condition
“he phased the intake with the output of the machine”