<span>The phase of mitosis during which the mitotic spindle begins to form is PROPHASE.
</span>At prophase, the nuclear envelope is broken down; the chromosomes disperse into the cytoplasm, condenses and become visible; and more importantly, the mitotic spindle fibers form.
</span>At prophase, the nuclear envelope is broken down; the chromosomes disperse into the cytoplasm, condenses and become visible; and more importantly, the mitotic spindle fibers form.