Exactly, and thats the issue, mobile phases usually last several seconds and even if in theory RDM can move 50% of the time, only has a GCD worth of time of free movement before being forced to cast again or lose damage. At best helps with minor positioning that shouldnt be needed once you know the fight. I would like for RDM to stop being considered the "training wheels" of the caster jobs, the Rez mage meme was quite sad
17-20 seconds on row of free casts >>> 2.X seconds after each 2.X second cast.
A simple moving phase example would be on Nier final raid with the flying 4 automata mobs that cast a huge aoe in front of them and the entire raid gotta keep moving behind each one. We are speaking of 10-15 seconds of "keep moving or stop cast a spell and eat a vul stack" and not even mentioning EX or raids/savage on wich the consecuences are far nastier than on a casual 24 man raid
Moving phases ironically tend to hurt RDM the most due to his mobility being extremely conditional on making a cast to get the dual cast instant spell