Why is my personal hotspot button not showing

Probably an issue with your service plan or carrier. Personal Hotspot is a carrier feature, the carrier must supported and it must be provisioned on your account.

Contact your cellular service provider and verify everything is correct on their side.

Link-> If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

Actually "Personal Hotspot" should normally be at the top level in Settings as well as inside Cellular:

That's where I see it on all my iPhones.

Because you must tap Cellular to find it. It is a cellular feature, and thus doesn’t appear at the top level menu in Settings.

If you don’t see it there, either than see Phil0124’s post above.

You are correct; I missed that.