This paper treats the phenomenon of phagocytosis from the flow of energy point of view. Considerable efforts have been made towards elucidating the subject of phagocytosis in other fields of learning, but little has been said about the mechanical work that is done during phagocytosis. Phagocytosis without doubt is an interaction that involves the flow of energy. Energy equation model of phagocytosis is then presented in this paper to analyze the mechanical energy that is involved in the build-up of the engulfment of bacteria by the phagocytes. Data of the E Coli bacteria from published work was then applied to the solution of the energy equation. A borderline contact angle of between the phagocyte and the bacteria at was deduced in this work. It was shown that when , , engulfment is favoured and when , , engulfment is not favoured for E-coli. This condition is conceptually in line with ΔFNET approach reported in the literature. Data of four different bacterial species were also used to plot the graphs of the engulfment parameter against contact angle which revealed that the more hydrophobic bacteria are easily phagocytized than the more hydrophilic ones.