Can I use iPhone data to access internet on iPad WiFi only?

The iPad can connect to the iPhone's Personal Hotspot, and use its Data plan yes. You do not need a cellular iPad.

See here:

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

Note that, the iPad will not limit its usage, and will attempt to do everything it does while connected to Wifi, when its connected to the iPhone. So unless you have an unlimited Data plan, its easy for the iPad to suck up all the allotted data very quickly. Pay close attention to the Data usage on the iPhone.

Also note that your cellular plan must be provisioned to support a hotspot, and it may not be free. Check with your carrier.