iCloud deleted photos not deleting from iPhone

I'm helping my father free up some storage in his iCloud. He deleted about 2 thousand photos but his iPhone still has it all.

According to Apple's documentation Manage your iCloud storage - Apple Support:

"Before you delete anything, make sure that you back up the photos and videos that you still want. When you use iCloud Photos and delete a photo or video on one device, it's also deleted on all other devices where you're signed in with the same Apple ID."

At first I thought deleting from iCloud would also delete from the iPhone but it doesn't seem to be the case. Does this mean it is only one way deletation? If I delete from iPhone it deletes from iCloud but if I delete from iCloud it does not delete from iPhone? Isn't my computer logged into icloud.com considered a device?

How should I mirror all the photos that were deleted from iCloud to his iPhone?