It is common practice, at least with respect to phos/calcitriol. We strongly recommend, however, that you transition your daughter to an endocrinologist with experience treating XLH adults to monitor her systems and to be prepared for burosumab to be approved by the FDA (assuming it is), so you can discuss whether ongoing treatment would be right for her.
The advice to discontinue phos/calcitriol after the growth plates close is NOT because the body no longer needs phosphorus, but because this treatment is not itself entirely benign -- there are potentially serious side effects (kidney calcification and elevated PTH) from the phos/calcitriol, so the risks and benefits need to be compared. Kidney calcification and elevated PTH do not appear to happen with burosumab, so the decision whether to continue treatment will be different in the future, and there appear to be significant benefits to maintaining phosphorus levels in adulthood. Phosphorus is not limited to use in bones, but plays a significant role in muscle development and function and also to energy levels. It's yet to be seen whether it will also help with dental and enthesopathy/calcification issues, but that's a possibility too.
Given that burosumab may well be available in just a few months (shortly after the FDA decision in mid-April), it's important to have a discussion with the doctor NOW about whether to transition to burosumab then, rather than to simply go off treatment altogether.
As always, I am not a doctor, just a patient, so you need to discuss the risks and benefits of each treatment option with your daughter's doctor. Even if you decide she should go off treatment, it's important to have your daughter monitored by an XLH-experienced endocrinologist for changes in symptoms, and not simply kicked loose as happens too often. It's common for patients to have symptoms appear again after they go off treatment, and you'll want to catch the change right away and have a doctor in place to deal with them. Too often, patients wait years (decades) before the symptoms get bad enough to go to a doctor, and by then the consequences (calcifications) can be irreversible.
There's a webinar on transitioning a minor to adult treatment (featuring one of our Scientific Advisory Board members, Maya Doyle) here:
https://globalgenes.org/rare-webinar-transition-of-care/
