Abstract: Millimeter-wave imaging technology has garnered significant attention in the aerospace industry for non-destructive testing of composite materials that are high-strength, low-density, heat-insulating, corrosion-resistant, and wave-absorbing. This is due to its exceptional object penetration capability and high spatial resolution in the near field. The imaging technique known as active reflective millimeter-wave imaging primarily utilizes the backscattering effect of near-field millimeter waves and objects to generate a high-precision image of the object under test. The imaging technique demonstrates its characterization capability primarily in two aspects: the inversion amplitude reflects the energy attenuation effect of the interaction between millimeter waves and objects, while the inversion phase characterizes the phase effect of the interaction between millimeter waves and objects. Current methods for near-field millimeter-wave imaging primarily rely on the attenuation effect of millimeter-wave energy to reconstruct the image of the object under test. This paper proposes combining phase imaging with near-field millimeter-wave imaging to enhance the precision of near-field imaging for non-destructive testing by utilizing the millimeter-wave object phase effect. The method proposed for near-field millimeter-wave phase imaging involves using a near-field two-dimensional synthetic aperture algorithm based on spherical wave decomposition to invert the phase principal value data of the reflectivity of the object under test. This is followed by reconstructing the high-precision absolute phase image of the object under test using a near-field phase expansion algorithm. Real tests were conducted on various specimens, including a metal mask, material sandwich, PTFE, quartz ceramic, and silicon nitride, to assess the feasibility of this method. The results indicate that the millimeter-wave near-field phase imaging method operating at 30 GHz to 40 GHz can effectively detect defects with a radius of 2 mm.