Hello radha1608,
Thanks for participating in Apple Support Communities. We understand that you're only seeing a small picture for your contact on incoming calls, instead of the full screen image you're expecting. Great idea with checking Settings > Phone, to make sure that "Full Screen" is selected and not "Banner". In your troubleshooting, did you try an entirely different picture to see if it appears as full screen? If the picture is too small, it will not appear full screen.
If that's not the case, turn the "Full Screen" setting to "Banner", then restart your iPhone and go back to choose "Full Screen" to see if that helps: Restart your iPhone
Let us know how it goes.
Take care.