Can’t see my number in my phone

Is your 8plus a "work" iPhone?

Check if you have a profile installed in Settings>General>VPN & device management

Shouldn't be this case, make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

Do you have a valid working Sim in the phone ?

The phone number should be input in Settings>Phone.

If thet option doesn't appear, check restrictions in your ScreenTime settings, or if your device is remotely controlled vy a company/school/institute, contact their IT admin/supervisor and ask them to remove MDM, if you're eligible.

Regards

Giulio