This answer is based on the understanding that outsourcing is a form of procurement, which is one of the knowledge areas in project management. Procurement involves acquiring goods and services from external sources to support the project objectives. According to the CompTIA Project+ Study Guide1, procurement activities occur mainly in the planning phase of the project, where the project manager identifies the project needs, defines the scope of work, evaluates the potential vendors, and prepares the procurement documents. The other options are not correct because:

Initiating is the phase where the project manager defines the project purpose, objectives, and deliverables, and obtains the project charter and stakeholder approval. Initiating does not involve procurement activities, although it may involve some preliminary research on the feasibility and availability of external resources.

Controlling is the phase where the project manager monitors and measures the project performance, compares it with the baseline, and implements corrective actions if needed. Controlling does involve some procurement activities, such as reviewing the vendor deliverables, managing the changes, and resolving the issues, but these are not the main tasks of procurement.

Executing is the phase where the project manager leads and directs the project team and other resources to complete the project work according to the plan. Executing does involve some procurement activities, such as selecting the vendor, signing the contract, and managing the relationship, but these are not the main tasks of procurement. References = CompTIA Project+ Study Guide: Exam PK0-005, 3rd Edition, Chapter 8: Planning Projects, Part 4 (Procurement and Communication), pages 243-260; CompTIA Project+ Certification Exam Objectives, Domain 2: Project Planning, Objective 2.5: Given a scenario, plan procurement for a project.