4. During what phase do centrioles begin to migrate to opposite poles of the cell?

Prophase

Explanation:

Prophase, the first phase of mitosis, is when the centrioles begin to move to opposite poles, the nuclear membrane disintegrates, the genetic material condenses, etc.

It could not be in metaphase or anaphase because the centrioles and spindle fibres have to already be established in order to line the chromosomes up along the equatorial plate, and then to pull the chromatids apart.