The phrase “John and Kerry are very good team players” is often used in a workplace to express they are willing to work for the team's good.

Yes, people use this phrase to express their work "with" and "for" the group. Teamwork is collaboration. It is a service to be there for your colleagues. It is the effort you and your group have to complete a task. It is also a group of people willing to work together towards something in common, like a goal. Now, what makes you a good "team player"? Click the link below and watch Simon Sinek talking about that. https://www.youtube.com/watch?v=zP9jpxitfb4