cut down (on something)
Definition: to reduce the amount of something you do or consume etc.
E.g.1: I was worried about my health so I cut down on the amount I smoke. Now I only smoke 5 cigarettes a day.
E.g.2: After his heart attack, his doctor advised him to cut down on fatty foods, alcohol and smoking, and to do a little more exercise each day.
This phrasal verb can’t be separated.