Unable to find my phone number in my iPhone

Tap on Settings > Phone. It should be listed after: My Number

If your SIM is activated then go to Settings > Mobile Data [There you have it]

The Find My app makes it easy to keep track of your Apple devices — even if they're offline. You can also locate items using AirTag or Find My technology. Plus, you can keep up with friends and family.

iCloud - Find My - Apple (IN)