How can I connect my iPhone to my iPad?

I suggest that you "force" restart both devices, then take a look at the following article just in case you missed something getting them set up to sync.

• Set up iCloud on your iPhone, iPad, or iPod touch - Apple Support

In addition you can also trying syncing them via a Mac or PC:

• Sync your iPhone, iPad, or iPod using your computer - Apple Support

What exactly are you trying to do that you need to connect your iPhone to your iPad?

To synchronize the data between your devices, both need to be logged in with the same Apple ID. Is this not the case for you?

I am having the same issues. Iphone 12 pro max will not connect to my ipad and keeps disconnecting from my macbook. icloud ids are signed in and are the same.