Tall plants in direct line of vision of a door or window is one of many ways to accomplish this. Use a phone headset to free your hands while on the phone.
Lightweight headsets are now available.
We are better at giving advice to others than to ourselves. You will come up with just the right answer to move through your own procrastination if you think of it in terms of what you might tell someone else. Estimate the time for a task and double it to accommodate interruptions. If you finish earlier than you estimated, it will fell like a bonus and a breather. Schedule cooperative time among secretaries.