my vet recommended the same,like others have said if their eating keep it goin. dont do what i did , and started reviewing and researching food,itll drive you nuts. not sure why vets recommend a high phosphorus food.
i only questioned it because i followed the food idm, may have that wrong , but hills royal and purina were rated so low. but a someone here sent a link, that shows who has hired vets etc.on staff and who owns/manufactures their own food, and tests them so that maybe more important?