Carrier wont blacklist stolen IMEI - any options through Apple ?

Several things are at work here:

If your iPhone or iPad is lost or stolen - Apple Support

1st - Your son’s phone is secured by his passcode. As long as it’s known only to him, the device is virtually impenetrable.

2nd - As long as the device remains on your son’s AppleID it CAN’T be re-used by anyone else. (A feature known as Activation Lock)

3rd - Beware of the criminals masquerading as Apple trying to phish your son’s credentials … they are NEVER from Apple.

4th - Carrier blacklisting is of only marginal additional value. Don’t loose any sleep over it.

5th - Your son does NOT need 2FA to “Mark as Lost” his phone: Simply browse to https://icloud.com/find. (DO include the “/find”)

6th - Your Son DOES need his 2FA verification code to add a replacement phone to his account. Your own phone might very well be setup as one of his trusted numbers to receive the code. (Simply click “Didn’t Receive Code” to see a partially redacted list of his Trusted Numbers)

See all options for 2FA code receipt here:

Get a verification code and sign in with two-factor authentication - Apple Support

That’s unfortunate.

Hope your son remained physically unharmed.

Best of luck with your carrier satisfying your insurer’s requirements.

Unfortunately, Apple plays no part in “Blacklisting” as that is purely a carrier function.

Apple’s “pieces” are the theft-deterrence features provided by Activation Lock and Stolen Device Protection.

(The latter — unfortunately — was apparently not pre-activated.)