lost phone / editing trusted #

My son lost his phone, we replaced it with another iPhone, while setting up it wants to send a code to old phone which of course we don’t have. He set it up with his trusted number being his own phone number (of course not how it’s supposed to be done)so we can’t get a code sent to the trusted number either, another option is to send it to his iCloud email which he has never accessed, & Possibly never enabled, but when we try to login to iCloud email from another device(my phone) It again wants to send a code to the phone or trusted number, So at this point we can’t even log into iCloud to edit the trusted number