Final answer:
The major portion of project work is done during the Executing Stage, which involves carrying out the project plan and coordinating resources to create the project's deliverables.
Step-by-step explanation:
The major portion of the physical and mental project work is performed during the Executing Stage. This stage is where the project plan is put into action and where the actual work to create the project's deliverables is carried out. It involves coordinating people and resources, as well as integrating and performing the activities of the project in accordance with the project management plan.
The Initiating Stage involves starting up the project, while the Planning Stage is where the project plans are developed. The Closing Stage is when the project is finalized and closed.