The paper presents a method for X-ray phase imaging using a high-efficiency grating interferometer and phase-stepping technique. This method allows the separation of phase and absorption profiles of bulk samples from a single set of measurements, enabling the reconstruction of quantitative three-dimensional maps of the X-ray refractive index with a spatial resolution down to a few microns. The interferometer consists of a phase grating and an absorption grating, which are used to create periodic interference patterns. By scanning one of the gratings and taking images at different positions, the phase information can be extracted from the intensity oscillations in the detector pixels. The phase-stepping approach, adapted from visible-light interferometry, helps separate the phase signal from other contributions such as absorption and illumination inhomogeneity. Tomographic reconstruction of the phase data yields the three-dimensional distribution of the X-ray refractive index, which can be used to distinguish between different materials with similar absorption properties. The method is mechanically robust, requires minimal spatial coherence and monochromaticity, and can be scaled up to large fields of view, making it suitable for use with laboratory X-ray sources. The paper also discusses the design and properties of the interferometer, including the optimal distances between the gratings, efficiency, and resolution limits.The paper presents a method for X-ray phase imaging using a high-efficiency grating interferometer and phase-stepping technique. This method allows the separation of phase and absorption profiles of bulk samples from a single set of measurements, enabling the reconstruction of quantitative three-dimensional maps of the X-ray refractive index with a spatial resolution down to a few microns. The interferometer consists of a phase grating and an absorption grating, which are used to create periodic interference patterns. By scanning one of the gratings and taking images at different positions, the phase information can be extracted from the intensity oscillations in the detector pixels. The phase-stepping approach, adapted from visible-light interferometry, helps separate the phase signal from other contributions such as absorption and illumination inhomogeneity. Tomographic reconstruction of the phase data yields the three-dimensional distribution of the X-ray refractive index, which can be used to distinguish between different materials with similar absorption properties. The method is mechanically robust, requires minimal spatial coherence and monochromaticity, and can be scaled up to large fields of view, making it suitable for use with laboratory X-ray sources. The paper also discusses the design and properties of the interferometer, including the optimal distances between the gratings, efficiency, and resolution limits.