How do I link my phone to my I pad

No iPad is an iPhone/smartphone.

To send/receive cell calls and SMS messages on an iPad, you need to pair/tether an iPad to an iPhone to be able to do this using cell call and SMS message forwarding.

Tap and read these links below.

Make and receive phone calls on iPad - Apple Support

Set up Messages on iPad - Apple Support

What is the difference between iMessage and SMS/MMS? - Apple Support

Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support

Good Luck to You!

What are you attempting to achieve by “linking” your iPad and your iPhone?

Are you trying to synchronise your data between devices? The iCloud User Guide may be helpful to you:

iCloud User Guide - Apple Support

Are you are trying to send or receive text messages from your iPad:

Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support

Perhaps attempting to access the iPhone hotspot for an internet connection when WiFi is not available?

How to set up a Personal Hotspot on your iPhone or iPad - Apple Support

Something else? With a better understanding of exactly what you are trying to achieve will help contributors to provide the explicit help or guidance that you seek.

To connect your phone to your iPad you need to log them into the same Apple ID.