Please clarify this request for us please, do you want to add additional fields to Maniphest? Or do you want to change how tasks look?

https://secure.phabricator.com/book/phabcontrib/article/feature_requests/

If you're talking about tagging a task, that's generally done in Phabricator using "Projects", which are like tags on steroids. (They're a little harder to create than in, say, JIRA, but otherwise work basically like tags/labels.)

Not only Using "Projects",

@chad Addition fields (Labels) , allow we add multiple labels , split labels with comma,

@staticshock , Tags will be very useful to identify the issue type and more detail information, and can be mark and then send to different department to resolve the issues.

for example, a issue with these Label:

SegmentFault,Kernel, OutOfMemory

can be send to kernel development work group.

Those are "Projects" in Phabricator. They act as general containers for labels, tags, teams, milestones, and projects.

You may also be interested in Custom Fields:

https://secure.phabricator.com/book/phabricator/article/custom_fields/

@chad i guess the Custom Fields will need more coding by myself. i do not like the way like this.
So i made a Feature request.
If Phabricator will built in with these support. we should save our time on it.