The phrase "is constant" can be replaced by a variety of synonyms to convey the same meaning. One such synonym is "remains consistent", which implies that something maintains its constancy without changing over time. Another synonym could be "stays the same", which highlights the idea of stability and continuity. Additionally, "unchanging" or "steady" can be used, which both suggest an unvarying state. "Enduring" also works well as a synonym, indicating something that persists or lasts, despite external forces. Lastly, "perpetual" could be substituted to suggest that the state of constancy is ongoing or everlasting. Ultimately, these synonyms all convey the underlying sense of something that is unwavering and unchanging.