Sounds like your photinia was subject to Entomosporium, a common leaf spot disease. This disease rarely kills the plant, but it is not attractive. In some cases, the disease can be so problematic that homeowners decide to remove the shrub. We do not recommend planting this shrub due to this disease.
The fungus overwinters in infected leaf debris (or on the infected leaves) Practice good sanitation. Rake and dispose of infected foliage, avoid overhead irrigation, also avoid mid summer pruning that may stimulate flushes of susceptible foliage and select resistant varieties when available. Registered fungicides may be needed on highly susceptible cultivars.
You will have to decide if you want to spray a fungicide. This is a preventative. It does not control existing conditions. Apply to the newly emerging leaves in the spring and periodically during the growing season. Follow label directions.
See our website for photos and more information http://extension.umd.edu/hgic/leaf-spot-photinia-entomosporium