Can I connect my iPad to my 5G from my iPhone if there is no WiFi available?

In absence of WiFi, your iPad can use the hotspot feature of a mobile phone (e.g., iPhone), or a Cellular Broadband Router (often known as a MiFi Router), to provide an internet connection via your Cellular Carrier's network:

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

That depends on whether your cellular service provider allows the use of the "hot spot" feature on your phone. Some plans include it for free, some offer it for an additional fee, and some may not allow it at all. Check with your provider.

If your iPhone and your iPad are on the same Apple ID or across Apple IDs in the same Family Sharing group, the connection can be quite simple.