You can find this exercise on page 63 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 tilt each foot side to side. Keep knees slightly unlocked. Repeat right and left weight shift 20 times. You should feel a stretch on the inside and outside of the ankles.