You can find this exercise on page 9 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: FLEXIBILITY, LEGS - FEET
Stand with feet in address position. Hands on hips. Lean, shift weight, and stand on toes, lifting heels. Then switch weight to heels and lift toes. Keep knees slightly unlocked. Repeat back and forth shifting weight 20 times. You should feel a stretch on the bottom of feet as well as back and front of lower legs.