Who owns this? This is the first question about any task. The answer is a name.
Point person. This is the one named person who handles an issue.
Go-to person. This is the person everyone turns to for a certain kind of problem.
On the hook. A person on the hook is personally responsible for a result. If it fails, the blame is theirs.
The ball is in your court. The next move is yours, and nobody else can make it.
That’s on me. The speaker takes personal responsibility for a mistake.
Too many cooks spoil the broth. Work with too many people in charge goes badly.