The main aim of the paper is paraphrasing Heidegger's category of being in the theoretic framework of Fregean phenomenological semantics. The choice of Fregean phenomenological semantics as the tool of paraphrase is justified by the fact that philosophy articulated in 'Sein' und 'Zeit' may be interpreted as the modification of Husserl's project of phenomenology which is treated, in turn, as generalisation of Frege's theory of sense and 'nominatum'. So in the paper it is defended that Heidegger's category of being stems from Frege's considerations devoted to the basic semantic questions. In the first chapter there are specified in existentialistic language ten principles clarifying the notion of being. In the second part the principles are paraphrased in the phenomenological theory of 'noema' (this category is understood in spirit of the so called Californian interpretation). This move allows us to show how the conception of being is the modification of Frege's and Husserl's sematics. In the last chapters there is re-constructed Heidegger's model of acts of reference. The formal tool of reconstruction is Lesniewski's formal language (enriched by Ajdukiewicz) with indexes designating ways of existence and referential backgrounds. The novelty of our approach to analytisizing Heidegger's existentialism resolves itself into the application of two new concepts, namely the concept of referential backgrounds and the concept of noetic moods.