The telephone squat
If you're caught on a long call or stuck on hold, take advantage of this time and do some squats.
Keep your legs shoulder-width apart, chest up, arms straight and balance your weight on your heels. Then push your butt back, keep your back straight and bend your knees until your thighs are parallel to the floor. When you come back up, make sure to squeeze those butt cheeks. Inhale when going down, exhale when coming up. Do this for 30 reps.