Existing self-tracking devices have been criticized for perpetuating a dualist, rather than phenomenological, understanding of the self as a separated mind and body. In this paper we answer calls for a phenomenological approach to the design of self-tracking devices. Ambient Cycle is a menstrual cycle tracking device that provides a continuous display of data in the home through coloured light. Through its design and long-term deployment, we found that a phenomenological approach facilitated; 1. the documentation of a diversity in subjective experiences of the enigmatic menstrual cycle; 2. the tracking of positive as well as negative aspects of the menstrual cycle, which challenges wider understandings of the body in society, and 3. novel uses of self-tracked data. We also expand on existing uses of phenomenological theories within HCI to include those that address interactions with the insides of our bodies.