More simple exercises are one leg squats -- if you use a desk to keep your balance, they're not that difficult to do and a great exercise you can do anywhere. Also, you can drop down and do 5, 10, 20 pushups anywhere. While on the phone you could put it on speakerphone and drop down and try to hold the plank position for the length of the call -- I've seen some Scrum meetings have everyone do the plank (shortens the meeting much more than just standing up).
A few more ideas :-D!