Think about what you are scheduling and how you manage interruptions.

People often schedule their work commitments and not personal ones. Whatever your idea of "break time" (a hobby, time with family or friends, workout, rest, etc): schedule that into your calendar as if it were a business meeting. Making it a regular time will help, for example every Tuesday and Thursday at the same time, etc.

Interruptions tend to be where most time ends up being lost, as they throw everything else off schedule.
It is ok to not pick up the telephone at that exact moment, or to not have an open door policy. Tell people to schedule their ten minutes to speak with you and when ten minutes are up, end the meeting. If they need more time they will learn to schedule more time.