Final answer:
According to Lippitt's phases of change, the action by the supervisor that reflects the final stage of improving the issue of ineffective communication among the managers is developing strategies to maintain the change.
Step-by-step explanation:
According to Lippitt's phases of change, the action by the supervisor that reflects the final stage of improving the issue of ineffective communication among the managers is option 3: The supervisor has developed strategies to maintain the change. This stage focuses on ensuring that the changes implemented are sustained over time.