Assuming it IS CKD, then it is at a very early stage and a restricted low-protein
diet is certainly not necessary. Lowing phosphorus in the
diet cannot do any harm, so this is worth pursuing - but do we know whether phosphorus is abnormally high in the blood? What do the blood results say? It is certainly not worth starting a binder at this early stage just yet.
Frankly, any vet that advises a DRY DOG FOOD for dogs that have or may have kidney disease is very bad.