What do you mean by unfolding of chromosomes. State the phase in which it occurs

During the prophase of the cell division,chromatin coils(folds) to form chromosomes.Folding is for equal distribution of Chromatin to both daughter cells. After the daughter chromosomes reach the poles the chromosomes unfold or uncoil to form chromatin.So unfolding of chromosomes means the chromosomes uncoil to give rise to thin and long chromatin.
It occurs in telophase of cell division.