Chromosomes condense, the nuclear envelope disappears, spindle fibers grow, and centrioles migrate to the poles of cell during the mitotic phase called

Prophase

Explanation:

The Prophase characterizes because the chromatin finishes the condensation process, which began during the final stage of the interphase.

Individual chromosomes are now visible to optic microscopy. Each chromosome is composed of two sister chromatids joined by a centromere.

During the prophase, the pares of centrioles separate, each of them migrating to opposite poles. The spindle fibers form. At this point, nucleoles have already disappeared. The nuclear membrane breaks and disappears too, and genetic material gets in contact with the cytoplasm.

helicase, i think thats it