The purpose of a user acceptance testing (UAT) phase in software development is to ensure that the software meets business requirements and is ready for deployment. UAT involves end-users testing the application in a real-world environment to verify that it functions as expected. This phase is crucial for identifying any issues or discrepancies before the software goes live, enhancing user satisfaction and minimizing post-launch defects. Successful UAT leads to increased confidence in the software's reliability and usability.