Respiratory monitoring is a long-term tracking activity, which can be used to detect breathing abnormalities in patients with chronic diseases and also to manage psychological stress. However, sophisticated and expensive medical equipment is not suitable and convenient for long-term breathing monitoring. Therefore, an affordable contactless sensing system needs to be developed for long-term patient monitoring. In this paper, we propose a new contactless respiration monitoring system using acoustic sensing with smartphones. We design several algorithms to find the relationship between chest movements and breath signals. Beyond breathing rate monitoring, our system can also provide detailed respiration patterns, including inhalation and exhalation time, and apnea time, which can be used for real-time respiratory biofeedback during meditation. Our extensive experimental results show that the developed system can track real-time respiration, thus enabling accurate respiration patterns monitoring.