Your mobile phone has a globally unique number associated with it, called the IMEI number, that uniquely identifies your device within the mobile network. If your phone gets lost or is stolen, you would need to provide this IMEI number to the law enforcement agencies and the telecom operator for them to blacklist your device and prevent anyone else from using your phone on their wireless network.
As you probably know, it is relatively easy to find the IMEI number of your mobile phone. While there are apps that will help you retrieve this number with a tap, you don’t really need one. Just open the phone dialer, call
*#06# and the IMEI number will be displayed on the phone’s screen. Alternatively, you can open device Settings - About Phone - Status and long-press the IMEI number to copy it to the clipboard.
If you have however lost your phone but did not record the IMEI number beforehand, you can still retrieve the number from your Google Account.
Just go to Google Settings, sign-in with your Google account and expand the Android tab. Here you will see of all Android devices that are connected to your Google Account and it will list the IMEI number of your phone as well.
In the case of iPhone, the IMEI number is printed on the box itself. And if nothing works, trace the phone’s receipt - the vendor may have written the IMEI number o the phone on it at the time of sale.
Update: A recent update seems to have dropped the IMEI number from your Google Dashboard.