The phrase "chafes at the bit" is commonly used to describe someone who is eager to do something, but is being held back. However, there are several other synonyms that can be used in place of this phrase. One of these is "itching to", which conveys a similar sense of impatience and excitement. Another option is "raring to go", which emphasizes the person's readiness and enthusiasm. "Antsy" is another synonym that can be used to describe someone who is restless and eager to act. Overall, there are many ways to express the idea of someone being eager and impatient, and choosing the right synonym can add depth and nuance to your writing.