my WhatsApp messages were not restored in my iphone

As you've been told already, you'll need whatsapp support to help you transfer your messages from an old phone to a new one. Generally, people here won't know how/where whatsapp messages are stored and backed up.

iCloud backup of them?

See WhatsApp support for help with their app’s built in backup and restore function -> https://faq.whatsapp.com/iphone/chats/how-to-restore-your-chat-history/?lang=en

Because they are not part of an iCloud backup. You must backup and restore WhatsApp data from within the WhatsApp app itself. That is the way WhatsApp has designed their app.

You may want to look at this article: https://faq.whatsapp.com/iphone/chats/how-to-restore-your-chat-history/?lang=en