How to get lost iPhone IMEI number without device box?

My sister lost her iPhone 14 Pro yesterday and unfortunately she cannot find her device box. So she cannot get the IMEI number for filing a case. The phone is already in Lost Mode from Find My app. The mobile network providers also cannot give us the IMEI numbers. Now is there any way we can email/contact Apple to get the code? We have all the necessary documents except the phone box.

[Re-Titled by Moderator]