It is possible to access the calendar from within a job or phase. The calendar button on both job and phase estimate tab will allow you to view existing bookings and, if you have the permissions to do so, make a new booking:
If you chose to view bookings the calendar is opened in a pre filtered mode to just show the bookings relevant to that job/phase.
If you have access rights to actually book items into the calendar you can select ‘Book into calendar’. The calendar is then opened in non-filtered mode (bookings for all jobs will be displayed), but the job estimate selection list below the calendar will be filtered to only show estimates / requisitions for this particular job/phase.
Note: Users can be given partial booking access rights. For instance, they may be allowed to create draft bookings only.