Hello,
Practically, if you use Scrum, there is no Project Manager titled person. Now if you talk about the "function" that a Project Manager does, that is does collectively as a team.
Principle 11 is Self Organizing and Self Managing teams - This is a major function of the project manager to manage. Sprint Planning is done with the involvement of everyone on the team. We have the Product Owner, who gives the Requirements which is managed using a Product Backlog. The Scrum Master is also the agile coach and he works with the Product Owner and the Team to ensure that any internal risks are mitigated and he protects the team from any distractions from external sources. Daily stands up and done and everyone is involved so risks are brought to the fore, discussed and everyone in the team is aware of the mitigation techniques that would be used so those who have done PMP know that 90% of the time of the Project Manager is spent in communication. So that is also a function of PM which is done collectively.
So if one is using Scrum then the function of a traditional project manager is done collectively by the team. Then again, the ideal scrum team should be between 5 to 9 people.
Cheers !!!
Elijah Nagawkar PMP, PMI-ACP, ITSM, OCP