Disable two-factor when I don't have an iPhone anymore

Until recently, I was using iMessage on both iOS and macOS. Now, my phone is dead with a black screen, so I did a full erase from iTunes. ("Find my iPhone" and iCloud is disabled on both devices.) Currently, I am still able to use iMessage from macOS. My iMessage account is connected only to my phone number, not my email address, and I'd like to keep it that way. My Mac and iPhone has two-factor setup, so you confirm stuff with the other device other. Since I now don't have an iPhone, how do I disable two-factor **without** breaking iMessage or anything?