"Get cold feet" is an idiom which means to suddenly feel nervous, hesitant, or unsure before doing something. There are a number of synonyms that can be used for this phrase, including:
1. Back out
2. Lose one's nerve
3. Get jitters
4. Feel apprehensive
5. Develop stage fright
6. Have second thoughts
7. Hesitate
8. Be reluctant
9. Pull out
10. Retreat
Using these synonyms can help add variety to your writing and make it more engaging. Each one has slightly different connotations, so it's important to choose the synonym that best fits the context and tone of your writing.