I have seen this issue three times. The first time the psql process had not completely halted and two psql instances were live and causing issues. The second time the port was never released and psql would fail to start because it couldnt attach to the configured port. The last time was because the file system had maxed out and psql was failing to start because there was no space to log.
As far as I can tell, you will only see this error when psql is down or unreachable via the configured port.
The easiest way to resolve it is to do a full bounce of the host that phantom is running on since no processes or port claims will survive, but if that doesnt fix the issue then you will need to take a look at psql logs and figure out why it is failing to start.
Its always possible that there is another reason that you could see this error that i havent encountered so please update here when you find the issue.