Open the Settings app
Tap About phone or About device
Look for Phone number or SIM status
Open the Phone app
Tap the three-dot menu or More
Select Settings
Check My phone number or SIM information
Open Contacts
Tap your profile or Me
Look for your phone number
Dial a friend or another phone and check the caller ID
Check the SIM card packaging or carrier account
Contact your mobile carrier if the number is not shown