First of all, you could try to stop all running servers:
sudo /opt/bitnami/ctlscript.sh stop
If Phabricator does not stop, look for all processes matching "phabricator" or "phd" and take the PID (second column):
ps aux | grep -i phabricator
ps aux | grep -i phd
With each PID (
THE_PID_NUMBER), execute this command:
sudo kill -9 THE_PID_NUMBER
Phabricator should not be running anymore, and you should be able to start it again.
Could you let us know if you had success?