The answer is anaphase.
Speaking of mitosis, which is a cell division of a single cell into two identical daughter cells, it consists of 4 phases - prophase, metaphase, anaphase, and telophase and cytokinesis. Chromatids are present only in metaphase and anaphase. During metaphase, sister chromatids join together. During anaphase, sister chromatids separate from each other to the opposite sides of the cell.
