Do you want your iPhone photo’s to be available in iCloud - where they can be accessed by other devices - or stored just on your iPhone?
If you want your iPhone photos to be stored on the iPhone and iCloud - but not on your iPad:
- iPhone: Settings > [Your Name / AppleID] > iCloud > Photos > iCloud Photos - set to ON
- iPad: Settings > [Your Name / AppleID] > iCloud > Photos > iCloud Photos - set to OFF
If you want your iPhone photos to be stored on just iPhone and not iCloud:
- iPhone: Settings > [Your Name / AppleID] > iCloud > Photos > iCloud Photos - set to OFF
- iPad: Settings > [Your Name / AppleID] > iCloud > Photos > iCloud Photos - set to OFF
In both cases, as Photos in iCloud is disabled for the iPad, your iPad photos will only be available on the iPad itself.