We investigate the axial phase evolution of light emerging from microstructures. The high-resolution interference microscope (HRIM) allows to record three-dimensional (3D) phase distributions in differential and propagation modes along the longitudinal direction. We apply this differential-mode HRIM to study the axial phase evolution of particular cases of microstructures, for instance, the photonic nanojet generated by a diecectric microsphere and the spot of Arago created by a micrometer-size metallic disc