Group velocity dispersion and normal, anomalous dispersion?

From my understanding, normal and anomalous dispersion are because the phase velocity is a function of k so it is different for different components of a group so the group will spread out over time.

So whats group velocity dispersion? Is it the same affect (dispersion/ spreading out) because of the group velocities being different? But if the group velocities are different wouldn't the phase velocities be too?

:confused:

Please help me understand!