During mitosis, it is necessary for the nuclear envelope of the parent cell to disintegrate. this is accomplished in part by phosphorylation of proteins associated with the nuclear envelope. if the enzyme responsible for that phosphorylation event is inhibited, at which phase of mitosis are cells likely to arrest?

Prometaphase

Explanation:

During prophase, chromatin condenses, so the chromosomes become visible, and once this is completed, it enters prometaphase (right before entering metaphase), where the nuclear envelope starts breaking down to allow the chromosomes to migrate to the equator of the cell, which occurs during metaphase. If the nuclear envelope doesn't break down, the cell can't continue into metaphase, so it is arrested at prometaphase.