After completing development and internal testing phases, the next step is to conduct User Acceptance Testing (UAT). UAT is performed by the end-users to ensure the system meets their requirements and is ready for deployment.
According to the CompTIA Project+ PK0-005 exam objectives, under Domain 2.3: Explain the importance of quality management and testing in project management, UAT is a critical phase to validate that the product meets the business needs and requirements.