In part, a PhD/MPhil is the creation of a “significant and original contribution to human knowledge.” 

A PhD/MPhil is also an “apprenticeship”, a time when a novice researcher learns the “tricks of the trade” (how to be a successful researcher) from an experienced researcher. This is simple in theory, yet how an “apprenticeship” works out in practice depends on the characteristics of the student and his/her supervisor. See Supervision for more.)

These two aspects are encapsulated in the University’s Statement of Research Higher Degree Graduate Attributes.