2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/90040We explore the role played by the phase in an accurate description of the entanglement of bipartite systems. We first present an appropriate polar decomposition that leads to a truly Hermitian operator for the phase of a single qubit. We also examine the positive operator-valued measures that can describe the qubit phase properties. When dealing with two qubits, the relative phase seems to be a natural variable to understand entanglement. In this spirit, we propose a measure of entanglement based on this variable.11 pages, previous title has changed, new section added, corrected typos, no figuresQuantum Physicstext