Hello and welcome to Apple Support Communities, jemimahissie!
I understand you're seeing a small contact picture when you receive a phone call instead of a full screen contact photo. I'd be happy to provide information to help you address this.
Make sure this contact photo is the one set with your contact in iCloud: Add a photo for a contact on iCloud.com
If this contact is stored with another email provider, it may not appear as normal. In that situation, your best bet is to export the contact from your email provider and then import it to iCloud. You can also opt to copy the information over manually.
I hope this helps.
Enjoy your day!