A concerned project team member complains to the project manager that another team member is...

According to the PMBOK Guide, the project manager is responsible for managing the project team and resolving any conflicts that may arise among team members. The project manager should use appropriate interpersonal skills, such as active listening, problem-solving, and negotiation, to address the issue with the disruptive team member and help them improve their performance and behavior. Providing team-building activities, informing the functional manager, or encouraging self-governance are not the best options, as they do not address the root cause of the problem or show empathy and support to the team member who is going through a difficult personal situation. References: PMBOK Guide, 6th edition, pages 349-350, 361-362.