We present the promising single- and multi-pass properties of a very simple Diffractive Optical Element which is a phase aperture. The latter is a two-level transparent phase-plate with a phase discontinuity of magnitude π. In the single-pass case the phase aperture can be used for laser beam tailoring. It is able to convert a Gaussian beam into a super-Gaussian, a ring-shaped or a doughnut profile, and an elliptic into a circular beam. In the multi-pass case the phase aperture is inserted inside an optical laser cavity in order to enhance some of its properties: transverse mode discrimination and fundamental mode volume.