User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-4563270-20150224205413/@comment-3253026-20150225003707

Then don't blow the Ultra discharge when the monsters up and moving? You can use back+X to just do the normal amped discharge when your shield's charged and it will still keep your shield boost and only use one phial. The Ultra's meant to be used when you've downed/stunned/paralyzed/sleeped/etc the monster and you know you can land it where you're aiming for. The windups ridiculously long on it because it's ridiculously high in KO and damage. Just check out the Nerscylla CB for use of the ultra discharge, the things got sleep on it so when you sleep the monster you can take a minute to line up the axe for the head. I think thats an insta-stun on a lot of monsters KO threshholds.

It seems like the problem you're having with it is just not using the back+X function. If you're using that it keeps your phials and your shield boost.