When you answer back you react to someone's criticism. Often in a rude manner.
It's not easy to give a certain synonym to 'answer back'. We can substitute this phrasal verb by 'object, mind, protest and retort'. But all of these verbs have additional specific meanings that should be checked.
Answer back in sentences
👉 She answered her mother back quickly.
👉 The teacher was angry when the student he was scolding answered him back.