The longest phase in the process of mitosis is called prophase. Even though prophase is the longest of all of the processes involved with mitosis, the cell remains in the interphase stage for a longer duration before the actual process of mitosis begins.
Prophase accounts for 14 percent of the time that the cell is undergoing the process of mitosis. During prophase, the cell undergoes several transformations that prepare it for cell division. Some of the most noticeable changes that can be observed are the disappearance of the nucleolus as well as the enlargement of the nucleus in preparation for division.