The term "most amphibious" can be replaced with several synonyms that describe different qualities associated with amphibians. Some alternatives include "most aquatically adept," which emphasizes their ability to navigate through water, or "most versatile in water and on land," which highlights their ability to adapt to various environments. "Most versatile swimmers" is another option that emphasizes their swimming abilities, while "most amphibian-like" focuses on their physical resemblance to amphibians. Overall, selecting a synonym depends on the specific context and desired emphasis, but there are many phrases that effectively convey the idea of "most amphibious".