Not entirely sure what you’re asking…
If an Apple ID issue… I’ll assume this is involving two-factor authentication, and that there are no other trusted telephone numbers, and no recovery contacts configured.
To regain access to an Apple ID in general, start here:
… How to use account recovery when you can’t reset your Apple ID password - Apple Support
In this case, you might be able to regain access to the Apple ID without resorting to recovery, with the cellular plan relocated to a different phone (swap the SIM) and by requesting the two-factor authentication code be sent to the phone number via text or phone call (use the “didn’t get a code” button). See:
… Get a verification code and sign in with two-factor authentication - Apple Support
If this is Activation Lock and a paired Apple Watch and an Apple Watch paired to a no-longer-available iPhone, see the “If you don't have your old iPhone or you erased it“ section here:
How to pair your Apple Watch with a new iPhone - Apple Support