Phabricator allows uploading images locally (to the separate domain phab.wmfusercontent.org, to be precise), and it appears that people find it useful to be able to illustrate tasks etc. in this way.
It would be nice to be able to embed images and other media from Commons, too, e.g. for charts, screenshots, mockups and screencasts. [[https://secure.phabricator.com/book/phabricator/article/remarkup/#embedding-media |According to the Remarkup documentation]], it's already technically possible to do that for YouTube (after setting a configuration variable), see also [[https://github.com/phacility/phabricator/blob/master/src/infrastructure/markup/rule/PhabricatorYoutubeRemarkupRule.php| source code]].
Besides avoiding extra uploading efforts for one's own files, this would also enable reusing freely licensed media by others from Commons, and enable reusing media from Phabricator elsewhere.
(Digression on licensing: The footer below optimistically claims "Content licensed under Creative Commons Attribution-ShareAlike 3.0 (CC-BY-SA) unless otherwise noted", but when I upload images here, I'm never asked to release that content under that license. So I'm kind of curious how that works legally. IANAL, but while the WMF Terms of Use specify licenses for text and - in the Phabricator ToU amendment - for code, they don't do so for other non-text media. In any case, a Phabricator media page - [[https://phabricator.wikimedia.org/F1207003| example]] - does not state a license and does not offer an option to specify an author separate from the uploader. Therefore it's not possible to satisfy the attribution requirements when reusing e.g. CC BY-SA media here.)
See also T76247