Prophase is where the cell is at rest. Interphase is where the cell membrane disappears and the chromosomes expand. Metaphase is where the chromosomes meet in the middle of the cell. Anaphase is where they are split apart. Telophase is where the cell begins to split. Cytokinesis is where the two new cells rest.
I believe you are talking about ANAPHASE. ANAPHASE splits the two sides of the chromosomes apart, which is duplication, so to speak.