The struggling Suns, owners of the worst record in the Western Conference, lost their fifth in a row.
Cousins had been over 30 points just once this season, having produced 31 against Toronto on Jan. 4. He hit 12-of-16 from the field against the Suns and made all six of his free throw attempts while adding 14 rebounds.
Sacramento built a 14-point halftime lead and easily held on while shooting 53 percent from the field.
Isaiah Thomas chipped in 23 points and eight assists for the Kings, who went 22-of-24 from the line.
Luis Scola led Phoenix with 25 points.