The lower potencies tend to act more like physiological doses. You may aggravate the patient, rather than curing.

The higher you go, the power of the medicine is enhanced and the ability of the medicine to heal becomes better. However, the vitality of the patient is to be kept in view, while giving higher potencies.

If you are sure the patient needs Phosphorous, better not to go lower than 200, give it in split doses, don't repeat unnecessarily, and wait for the reaction.

Murthy