Can you post a picture pumpkin, click on the green tree icon above the dialogue box.
Photinia are usually trouble free so this could be interesting.
Just above where you write the text is a small icon to the right hand side that looks like a little tree, thats the insert image icon. I just read on another message the icon does'nt show up if you're using a phone to post.
As for Photinia they can be prone to leaf spot which looks like this:
If it's that then it's a fungal infection and there's a few things you can do:
You should Plant photinia in full sun and provide good air circulation, if they're planted too close to something else then you can get this problem. Thinning them out a bit can help the air circulate better and their neighbors too if they're too close.
Remove and destroy fallen leaves, prune off diseased twigs.
Avoid watering over the top which keeps leaves wet for long periods of time.
You should also spray it with fungicide, copper but it needs multiple applications. It also depends (if this is the problem) how badly the plant is affected as it can be quite difficult to get rid of once it takes hold.
If it's a young plant I would'nt cut all the leaves off as that might weaken it more. For now I'd collect up any leaves that drop off and get rid of them and when you do water it make sure you water from underneath the foliage rather than over the top.
Make sure the pot has decent drainage so if it's sat on the floor you could raise it a bit with pot feet or something similar. You want the soil to be moist but not for the plant to be sitting in water all the time. Also make sure the pot is big enough for the plant, a small pot could be stressing the plant making it more open to disease.
Photinia's are fairly tough but fungal problems can be a real pain to control. You'd probably have to look at just controlling the problem this year by getting rid of the fallen leaves and keeping an eye on the watering. Next year when the new growth starts keep up the monitoring, remove the old diseased leaves if the plant is putting on good new growth and apply a fungicide regularly as a preventative measure as Buddyboy has said, it only works to protect the new growth.