The upgrade phases are listed in the left pane of the Windchill Upgrade Manager. Each Upgrade Phase contains a number of upgrade tasks. An upgrade phase gets marked complete if all the tasks in that phase complete successfully. Some upgrade tasks cannot be re-run. That is, if a task that cannot be re-run has completed successfully, but one of the other tasks failed in that phase, then the non-re-runnable task will not be re-executed if the phase is run again. Such tasks will be marked as skipped tasks.