Googling came up with:
If you have 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.
Tech, a la carte
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And from Apple:
If you don't have your device
There are several places to check that might show the serial or IMEI/MEID number.
- Go to appleid.apple.com in a web browser.
- Sign in with the Apple ID that you use on your device.
- Choose the Devices section. To see the serial and IMEI/MEID number, select the device.
Learn how to find the serial number, IMEI/MEID, CDN, and ICCID on your iPhone, iPad, or iPod touch.
support.apple.com