I used to see my contacts' photos full screen when they called or when I called them now I only see a thumbnail when they calling and when I call them.
Have you synced your address book with GMail? It usually does it.
It was found earlier that if you add photo to the contact through iPhone it will display them full screen. And if you add it from address book app from a mac it will display them small.
Now I heard syncing contacts to iCloud will do just the opposite i.e. it will force all the contacts to be displayed full screen. Though I did not try. Try to sync to iCloud if you can and report back.
I just chatted with Apple support. This is a change that was done with the last update. They said there is no work around to fix it, but said to please go to Apple Feedback on their site and let them know you want the FULL SCREEN pics back. The more people that complain, the more of a chance there will be that they will change this!
I, for one, can hardly even see the tiny little pic icon that they changed it to! When the pics were full screen, they were easy to see, even if you were even a few feet away from your phone! PLEASE SUBMIT FEEDBACK so they will change it back to the old way.