Final answer:
In the procurement process, the controlling phase is when a project manager reviews a vendor's performance and checks if milestones are being met. This phase is crucial for ensuring vendors adhere to contractual obligations and for making adjustments to maintain project objectives.
Step-by-step explanation:
At which phase in the procurement process would a project manager review a vendor's performance and determine if they are meeting milestones? The correct answer is b. Controlling. During the controlling phase, the project manager actively monitors vendors and suppliers to ensure that contractual obligations are being met, including the achievement of specific performance milestones. This is a key part of project management, where performance reviews and metric evaluations take place to maintain control over the procurement aspect of the project. It ensures that the vendors are on track with their deliverables, and it allows for adjustments to be made if necessary to meet project goals.