If you're searching for an alternative phrase for "performing poorly," there is a wide variety of options available to use instead. Here are a few examples you may find useful:
1. Failing to meet expectations
2. Underachieving
3. Delivering substandard results
4. Falling short
5. Not living up to standards
6. Poor performance
7. Unsatisfactory output
8. Doing badly
9. Inadequate progress
10. Disappointing performance
All of the options above convey the same general idea: that someone or something is not meeting the desired criteria or expectations. Choose the word or phrase that best fits your situation, either to use in your writing or in your daily conversations with others.