The SSH Troubleshooting steps at the end of this article (https://secure.phabricator.com/book/phabricator/article/diffusion_hosting/) should include the following suggestions:
1. Check your `phabricator-ssh-hook.sh` file for proper settings.
2. Check your `sshd_config.phabricator` file for proper settings.
As a native English speaker, I naturally skimmed over the part telling me to not only copy the `phabricator-ssh-hook.sh` file but to **also edit it to have the correct settings**.