Final answer:
A cooperative fellowship is best described by a phrase indicating a group formed on the basis of voluntary mutual agreements for the betterment and support of its members through mutual interdependence.
Step-by-step explanation:
The phrase that best describes the nature of a cooperative fellowship is 'A fellowship based upon mutual agreements voluntarily entered into by the membership'.
This type of fellowship is characterized by the presence of organic solidarity, which emphasizes mutual interdependence and cooperation.
Such fellowships are formed when individuals or groups engage in the exchange of products or services that are based on mutually satisfactory contracts, promoting a social cohesion built around shared goals and interests.