I think when an admin creates a repo in gerrit that the steps also include creating a repo in phabricator. It would make the migration easier and since we changed the gerrit links to phabricator the revision won't link to the correct repo.
Also as part of that process I think they should also update the redirection script and add the new repo that can be redirected.
This needs updating https://www.mediawiki.org/wiki/Git/New_repositories/Requests
To explain that when creating a repo in gerrit they should also do it in phabricator and set it up so it mirrors the repo from gerrit like git.wikimedia.org does.
Also the redirection script at https://gerrit.wikimedia.org/r/#/admin/projects/phabricator/extensions would need updating for the new repos.
So I think the user that has admin right at gerrit to create the repos should for both phabricator and that project that uses the redirection script so that it is done in one process.