You can find your own phone number either through the settings option of your phone, which is different depending on the operating system installed on your device, or by calling another phone. Generally, calling another phone can be a simpler solution when you are trying to find your phone number as the caller ID usually displays phone number information.
If you have another phone easily accessible, use your charged phone to call the other phone's number. First, make sure that the other phone has a caller ID. Once you call the other phone, look at the number that appears on that phone's missed call information. That number will be your phone number.