In the end of June 2016, a phabricator upgrade shifted the terminology away from blocked/blocking in favor of parent/subtask. Our phab help pages on wiki need to be updated to reflect this.
https://www.mediawiki.org/wiki/Phabricator/Help#Blocking_tasks (needs a rewrite)
https://www.mediawiki.org/wiki/Phabricator/Project_management#Tasks_that_cannot_be_worked_on_yet (needs rewording)
https://www.mediawiki.org/wiki/Phabricator/Project_management#Scope_of_tasks (probably just remove quotes around 'subtasks')