In the condole logs, it appears that the following is output no matter what the state of phpCollab is.
phpcollab_1 | WARNING: unable to establish a database connection to 'db'
phpcollab_1 | continuing anyways (which might have unexpected results)
https://github.com/phpcollab/docker/blob/master/docker-entrypoint.sh#L175-L178
I get it when phpCollab failed to properly install itself, and I also got it when phpCollab was successfully installed.