There are a total of 29 locations for the KRN23 adult clinical trials across the globe now (some not yet recruiting, while they wait for local approvals, but you can contact them now to let them know you're interested when the location is fully set up), including eight in the U.S., two in Canada, one in Denmark, three in France, five in Japan, two in Korea, six in the UK, and one each in Denmark, Ireland, and Italy.
You can get all the details here (age 18-65, regardless of past treatment): https://clinicaltrials.gov/ct2/show/NCT02526160?term=xlh&rank=1
or here (age 25-65, no treatment in past two years): https://clinicaltrials.gov/ct2/show/NCT02537431?term=xlh&rank=2
As always, the XLH Network, Inc. does not endorse or critique specific clinical trials, and does not counsel individual patients either for or against participation in any specific clinical trial. Prospective volunteers should always carefully review the clinical trial's informed consent documentation, and discuss the pros and cons of their participation with trusted advisers, including their health care providers and family members.