You could work with dumbbells using one or both hands when listening to conference calls. It's good to get up and move around a bit regularly, so one can make a point to do ten pushups, burpees, or jumping jacks every time you start to step away from your desk. Small sets of exercise add up and can be very beneficial.
http://lvb.link/2hBRpjV (shortened Dropbox link, to a picture)
I walk in 25 minute segments, then take 5 minute breaks. Then I take longer breaks at intervals. (Pomodoro Technique)
When I'm tired, or when I need deep focus... I switch to sitting mode, and lower the desk.