it is some what true, Den is taller and bigger, and require more sun light and nutrient, thus grows faster. However, I don't say that a phal is a slow grower either. They're very different in growing habit and you cannot really compare them with each other. Phal will only grow vertically (taller and taller) while Den can grow taller but has a certain limit and will stop growing when it reach the tip, after that Den can sprout out new canes at their feet. Therefore there's at least 2 factors right there:
1) Den has to reach maturity of each cane quicker while Phalaenopsis doesn't have to do it because it can flower on a side.
2) Den takes more light, thus grow faster
There.