My phone isn’t getting cellular network.

Okay, start here:--> If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

If you get no help, use the link (written in blue in the last line of the article "Contact Apple Support").

Regards

Giulio

To be sure, you can install a fresh copy of iOS on your iPhone, performing these steps:

Create a full backup of your iPhone, then restore it to factory settings and, in the end, set it up as new, using this support guide:--> Restore your iPhone, iPad, or iPod to factory settings – Apple Support

When done, test your device for a while, without restoring data from backup. If everything is okay, you can exclude a hardware issue.

Restore data from your previously made backup:--> Restore your iPhone, iPad, or iPod touch from a backup

Regards

Giulio

What error message are you getting?

That's a warning / error message. Could you please copy the complete message? and post it ihere?