On most phones, you can find all the relevant serial numbers in the same location in your Settings. Check in one of the following places, depending on your phone model:
- iPhone: Settings → General → About
- Android phones: Settings → About Device → Status
- On the Samsung Galaxy and some other models, you'll need to click More in the Settings menu before you can reach About Device.
- Lumia phones: Settings → About → More Information
- Nokia X phones: Settings → About Phone → Status