the phone DOES NOT ring

Turnoff Silent mode. How to put your iPhone on vibrate, ring, or silent mode - Apple Support

Contact Apple. Contact Apple Support

If you need the manual see (link) https://help.apple.com/iphone/12/ for the online version. If you want it offline there’s an iBooks version https://itunes.apple.com/book/iphone-user-guide-for-ios-12-1-1/ which you can load to your new phone.

Feel free to come back and post with questions if you can’t find the answers easily.

For the ring issue, there are 3 possibilities:

• There is a Mute switch on the left side of the phone near the top. It will mute everything except alarms it it is on (pushed toward the back of the phone), and it will show red if you look in its slot. Move it towards the screen if it is back and showing red.
• Just below the Mute switch are volume buttons. The top one is Volume Up (as you would expect). With the Home screen displayed these switches control ringer volume. (They control the volume of whatever app is currently open at other times.)
• There is a feature called Do Not Disturb, which suppresses all sounds when it is on. You control it in Settings/Do Not Disturb.

If your phone isn't sending Caller ID go to Settings/Phone and turn on Show My Caller ID. If that does not resolve the problem your account is not provisioned correctly. Contact your carrier to resolve it. Note that iPhones do not display the name of the caller unless the caller is in your Contacts. It will display just the phone number if the caller is not in your contact.

Check the Silent switch, usually left side near the top of the screen. IPhones are unusual in current phones by having a hardware switch for Silent rather than on screen operation.