Prophase, metaphase, anaphase, and telophase are the four main stages of mitosis, or the process of a cell separating its replicated chromosomes into two separate nuclei for cell division. The longest phase is prophase. This is when the nucleolus and nuclear membrane begin to disappear and the centrosomes are pulled to opposite ends of the cell via microtubules. Metaphase is when the centromeres on the chromosomes line up between the two opposing centrosomes. Anaphase is the shortest phase of the process. This is when the replicated chromosomes separate and are pulled by the microtubules to the opposite centrosomes. Finally, telophase is when the new nuclear membranes start condensing and two new nuclei are formed. The cell also prepares for cytokinesis, or final separation into two new cells.
So the longest phase is the prophase and the shortest phase is the anaphase.