With the latest iOS version on your iPhone too you can get a full screen image of incoming call contacts but the hacks are for iOS 14 mainly. The latter version from Apple introduced the banner image display format. This could be seen as an effort to ensure users do not get disturbed by incoming calls while they are busy with some other task on the iPhone.
What Users Want?
However, numerous internet threads and conversations going around suggest that users still want full-screen picture in iPhone phone calls instead of the small banner icon. This actually helps with both the iPhone Mini and the iPhone 13 Pro Max given that both models make users miss calls often. Additionally, Messages and Remind Me functions are not available at your fingertips. Here is the easiest way to set a full screen image for iOS 14 but this works on both iOS 12 and 13.
Adding Contact Photo on an iPhone
If you have got an earlier model such as iPhone 8, select Contacts and pick one. Select a photo by clicking Add Photo from Edit link. This is a safe and easy method to add a relevant picture to any saved contact.
Alternatives For Full Screen Picture in iPhone Phone Calls
There are third party applications too that help you sync social media clicks with saved contacts on iPhone. Ensure the safety features are in place before you begin to use one though. You can always use a third party application from the official App Store though. Sync.me is one such app that allows you to save images that are imported for addition to a saved contact, from a linked social media profile. The free version is high on advertisement count but you can make a referral and earn the Pro version for a month. Even after you delete the app, the full screen picture in iPhone phone calls still appears. You may even edit the image later and the full screen picture still keeps appearing.