Phone App

You can’t delete something you’ve never had. The Phone App is only found on iPhone.

An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. An iPad is not, and can never be, a standalone substitute for an iPhone.

However, If paired with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s continuity features.

More information about Continuity and the relevant Cellular services can be found here:

Continuity

Use Continuity to connect your Mac, iPhone, iPad, iPod touch and Apple Watch – Apple Support

SMS/MMS Messaging

How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

WiFi Calling

Make a call with Wi-Fi Calling – Apple Support

There is no Apple "Phone App" associated with the iPad. Perhaps Make and receive calls on your Mac, iPad, or iPod touch - Apple Support will help you find what you are looking for.