In what phase of mitosis does the nuclear envelope dissolve?

During prophase, the nuclear envelope dissolves as part of the preparation for cell division. This phase marks the beginning of mitosis, where chromatin condenses into visible chromosomes. As the chromosomes become more distinct, the nuclear envelope breaks down, allowing the spindle fibers to interact with the chromosomes. This dissolution is a critical step that facilitates the proper alignment and separation of the chromosomes in the subsequent phases of mitosis. Without the breakdown of the nuclear envelope in prophase, the chromosomes would remain enclosed, hindering their movement and organization for division.