Conpherence is a Phabricator application that allows users to have private communications 1:1 or in small groups. You can try it out at https://phab-01.wmflabs.org/conpherence/
Wikimedia favors public communication everywhere, and this is the main reason why we don't have it enabled here. However, in several discussions about onboarding and retaining new contributors we have concluded that the imposing public-only approach together with the difficulties to establish more intimate circles is a major problem for newcomers indeed.
So why don't we try an experiment? Let's enable Conpherence only to the members of a #FOSS-OPW-9 project (interns + mentors + Developer-Advocacy team) and let's run a test between 12 November and the end of March (see the program timeline).