The IMEI number uniquely identifies your mobile phone on the network. Learn how to find the IMEI number of your mobile phone after it is lost or stolen.
our 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.
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.com/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.