Final answer:
Lessons learned are established during the post-implementation phase, where project teams review and reflect on the project's successes and areas for improvement.
Step-by-step explanation:
Establishing lessons learned typically occurs during the post-implementation phase. This phase serves as an opportunity for project teams to reflect on what worked well and what could be improved for future projects. Applying lessons learned is a key principle in project management and continuous improvement endeavors, encouraging the adaptation of strategies and processes based on real-world experience. Lessons learned can be captured through various methods, including project debriefs, retrospective meetings, or post-project reviews, and they contribute to organizational knowledge and the enhancement of future project outcomes.