Can I share my iCloud storage from my iPhone to iPad

iCloud storage is automatically available to all devices that are signed into iCloud with the same Apple ID; i.e., it is linked to your Apple ID, not to a specific device.

Yes, when both devices are signed in with the same Apple ID & password.

The same 5 GB free for both devices, or you can subscribe to 50 GB, 200 GB or 2 TB iCloud Storage.