When a 9-month-old baby has cough and phlegm, different methods of treatment can be used according to the specific situation: 1. If the child only has a mild cough and phlegm, such as coughing occasionally a few times a day, no special treatment is usually needed, but the child needs to drink more water or fresh fruit juice and add fruits such as apple puree to the supplementary food. 2. If the symptoms of coughing and phlegm are serious, such as frequent coughing and phlegm, or even affecting sleep, the child needs to be treated with medication under the guidance of a doctor in a timely manner.