The m phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, then

The cells would most likely get arrested in the metaphase stage.

Explanation:

Certain points found in the cell cycle of eukaryotes, at which the advancement of the cell to the next stage of the cycle can be prevented until and unless all the conditions become favorable are known as the check points. One of these checkpoints is the M checkpoint, which is found close to the termination of the mitosis metaphase stage.  

It is also known as the spindle checkpoint as it determines the accurate attachment of the sister chromatids with the spindle microtubules. At the time of the anaphase stage, the distinction of the sister chromatids is an irreversible step, thus, unless and until each sister chromatids pair are attached strongly with the spindle fibers originating from the reverse poles of the cell, the cycle will not progress further.  

Therefore, if all the chromosomes are not attached to the mitotic spindle the M checkpoint will not allow the cell to go the next stage and will arrest the cell in the metaphase stage.  

The M phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, then the cell will be arrested in metaphase.

In conclusion, the M phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, then the cell will be arrested in metaphase.

Learn more about the M phase here: