..if the source below is anything to go by:

"The acceleration phase represents the interval
from the previous phase to ball contact."

Or failing that: "Early follow through"

"Early follow through represents the interval between ball contact and the point where the club is again horizontal to the ground,
but this time on the upward swing."

But in the final analysis, it all depends how technical you want to be. I am sure you can use something more colloquial that would be understood equally well in the context.