I got a new phone because my last one was stolen and it won’t allow me to sign into my iCloud what can I do

I got a new cell phone in the mail because my last one got stolen. When I sign into iCloud it’s saying that it’s sending me a passcode to continue signing in to my phone that I do not have and I’m not receiving a text message on the current phone that I just received to replace my old phone. What can I do to fix this problem