Final answer:
The phase described is Metaphase, the stage of mitosis where chromosomes are maximally condensed and align in the middle of the cell for separation.
Step-by-step explanation:
The phase where chromosomes line up in the middle of the cell and microtubules attach to the centromeres is called Metaphase.
During Metaphase, sister chromatids align along the metaphase plate, which is situated between the two poles of the cell. This is the stage of mitosis where chromosomes are maximally condensed and the microtubules are prepared to separate the sister chromatids and move them to opposite sides of the cell.