I've just added a new status which can be applied to phabricator tasks.
It is now possible to explicitly mark a task as "In progress" to indicate
that you are working on it. This is in response to some Wikimedia teams
using a workflow that involves assigning tasks before work begins. Once
work begins in earnest, you can now make that status change explicit by
marking the task with the "In progress" status. Functionally it's
identical to "open," however, this will allow for some improvements to
progress tracking and reporting.
Feedback about this change can be submitted to Phabricator on the task[1]
[1] Evaluate adding "In progress" status to Phabricator.
<https://phabricator.wikimedia.org/T288956>