Lost phone/Stolen

You can log into www.icloud.com/find without being asked for a two-factor code.

You can also log into www.icloud.com (without the /find) and when asked for the code, ignore it and click the Quick Access to Find My button instead.

Also note that even though you can do the above without a code, I would strongly recommend having multiple trusted phone numbers. The can be Androids, landlines, friends or relatives. See the following for more information: Two-factor authentication for Apple ID - Apple Support

If you don't have access to any trusted devices and you don't have access to any trusted phone numbers, see the instructions in the Frequently Asked Questions section of Two-factor authentication for Apple ID - Apple Support