The command for "Composer" under https://www.mediawiki.org/wiki/Continuous_integration/Phan#Running_Phan does not work here (though I set up Phan with Composer on Fedora 25).
[acko@canis mediawiki-core]$ pwd /home/acko/coding/mediawiki-core
[acko@canis mediawiki-core]$ PHAN=/home/acko/coding/mediawiki-core/vendor/etsy/phan/phan /home/acko/coding/mediawiki-core/tests/phan/bin/phan fatal: Not a git repository (or any parent up to mount point /home) Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set). Could not find a phan config file to apply in /tests/phan/config.php
Obviously, /home/acko/coding/mediawiki-core/.git/ exists.