The own phone number is displayed or hidden on the Samsung device by default according to the standard settings of the network provider. Normally, this means that the phone number (caller ID) is transmitted to the other party. However, in the settings of the phone app it can also be clearly defined whether the phone number should be displayed or hidden.

Android 10 (One UI 2.0)
Step 1:  Open the  Phone App
Step 2:  Open the  Menu
Step 3:  Tap on  Settings
Step 4:  Tap on  Supplementary services
Step 5:  Tap on  Show caller ID
Step 6:  Choose between  Network default ,  Hide number  and  Show number
  1. Open the Phone App
  2. Open the Menu
  3. Tap on Settings
  4. Tap on Supplementary services
  5. Tap on Show caller ID
  6. Choose between Network default, Hide number and Show number

Samsung Instructions