Hello santhan2695,
Thanks for this post to Apple Support Communities. We have some suggestions for photos saved for contacts not showing as fullscreen.
First, are you adding photos to your contacts directly in the Contacts app, or are you doing it another way?
Try to add the photo using the Contacts app with these steps:
Edit contacts on iPhone
The photo you choose must already be in the Photos app or be taken at the time you are adding it to the contact. Keep in mind that the size of the image when you receive a call will depend on on the size and resolution of the image in the Contacts app. Photos that are relatively large and high resolution should show full screen during the call.
Photos that are either taken with zoom in the Camera, zoomed when selecting the portion of the image to show for the contact or from a Contact server such as iCloud may appear in a circle rather than being fullscreen.
If the original photo is smaller or lower resolution to begin with, that may be the reason. You might need a new photo for that Contact that starts out larger and higher resolution to use for their Contact Card.
Take care.