Can I report my phone stolen with the imei number?

Click on this link and read it to find out what to do "If your iPhone, iPad, or iPod touch is lost or stolen" --> https://support.apple.com/HT201472

- The Find My service is the only recovery feature Apple offers. It MUST be set up before the device is lost. If you did not do that it is too late to do it now and there is no other feature Apple offers that can help you find it.

You can contact your carrier and ask them to blacklist the IMEI. You will need to prove to them that you are the legitimate owner of the phone.

Report it to whom? If you wish to report the theft of your iPhone to law enforcement, they generally want the serial number. Apple does not take reports of stolen phones.