Hello. You can't say "¿Cómo llamas?", if you don't use the reflexive noun, you change the meaning of the question. Concretely, in that question "¿cómo te llamas?" means "what is your name?"; but "¿cómo llamas?" means something like "how do you call?". For example, in a phrase, "¿cómo llamas (a casa)?", " How do you call (home)?".