At the end of the design phase it is advisable to draft a "scoping document" describing and explaining the major decisions. This document does not need to be long or highly formalised. Its purpose is to secure and strengthen the common understanding that has been achieved between the sponsor, coordinator, team, main stakeholders and maybe even already a number of other groups. This document can subsequently be used as a reference point throughout the exercise.
Writing up the document also requires a first feedback loop including all the actors involved at this stage of the exercise.