The phrase "is based" refers to something that is founded or built on a particular concept, idea, or principle. There are several synonyms for this phrase that can be used to convey the same meaning. Some common synonyms for "is based" include "rests on," "relies on," "depends on," "hinges on," "centers on," "revolves around," and "is built upon." Each of these phrases can be used to describe a specific element or aspect that makes up the foundation of something. By using these synonyms, writers can add variety and depth to their language and communicate their ideas more effectively.