This article presents the Husserlian conception of arithmetic, based on its psychological and phenomenological analyzes. Our goal is to analyze what Husserl presents as a structure of subjectivity, through the experiences of number consciousness. We start from the logico-psychological problems linked to the foundation of mathematics to restructure the subjective substance that governs the conceptualization of scientific foundations; we go through representative psychology to measure the objective dimension of arithmetic and see that number, as quantity, proceeds from a psychic construction. We clarify the path followed by Husserl in the development of phenomenology as a descriptive science, where subjectivity is a condition for the possibility of knowledge. We arrive at the result according to which, scientific objectivity is the corollary of a subjective a priori.