Phabricator code only supports CircleCI api 1.0, which doesn’t exist any more.
The only other integration built by Phabricator team is “Buildkite”, which I can honestly say I have no information about.
The other approach is to build some integration on your end using the “make HTTP call” build step: HM makes a call to the CI system, and the CI runs the build and calls back to tell HM that it’s done.
in https://secure.phabricator.com/T9456 you may see some options about integrating other CI systems using tools other than “official support”. Uber’s Jenkins Plugin is probably the most used integration plugin for CI.
It’s also possible to use HM with Drydock as your CI pipeline, but it’s more complicated (I don’t know if anyone is using it other then the upstream).
If you can switch to another CI, it might make sense to use one of the things listed in T9456. If you have to use CircleCI, you’ll need to get some things to work in a new way - either by writing a gateway service to mimic CCI 1.0, or by making some local changes to Phabricator to make it work.