If you’re settling in for a couple of hours of deep work with a Facebook tab open, your ‘phone ready and willing to accept calls, and your colleagues feeling like they can interrupt you at any moment, you’re setting yourself up for distractions.
Make sure people know they shouldn’t disturb you (wearing headphones can reduce interruptions dramatically). Turn the phone off. Sign out of social media. Close all unneeded tabs, and concentrate on the task at hand for the time period assigned to it. You’ll often be surprised at how much you get done.