Counterstance is only useful for other jobs that don't have retaliation. You're actually hurting yourself quite a bit by using it on WAR (for skilling up purposes, that is to say.) If you have a healer that allows you to go WAR/MNK, 50% Retaliation + 10% Counter rate => 55% chance of striking back at the mob. If you activate Counterstance, your Counter rate goes up to 50% which will produce an overall 75% chance of striking back. However, flooring your defense means you can only pull about half or less of the mobs that you were before. So while your chance of striking back may have risen by a marginal 35%~, the occurrences for this to occur has dropped by at least a factor of 2. It's not worth it. You can literally fight every single Fear Dearg in the zone with Phalanx + PDT, so if you have a healer to assist you then you should be doing that.
Also, for those who might have trouble recasting Phalanx if you're WAR/RDM. There is a trick to it. You need to get yourself up against a wall and then move back a little bit (hugging the wall.) This will actually cause all of the mandies to gather at almost the exact same spot right in front of you (which is good for Retaliation anyways.) Then, when you need to recast, run backwards a bunch and begin casting. Their pathfinding gets really jacked up and it takes them about 10 seconds to start hitting you again.