iCloud issues on my new iPhone
The first piece of the puzzle for you is to get your list of trusted devices and trusted phone numbers updated. 


https://support.apple.com/en-us/HT204915


Be aware there is an older two-step process and a newer two-factor process so I usually print out the article and keep notes when helping someone so we don’t go down the wrong path for the other process. 

The FAQ at the bottom of the article might cover your exact situation, so start there.