We present a full-field phase microscopy technique for quantitative nanoscale surface profiling of samples in reflection. This technique utilizes swept-source optical coherence tomography in a full-field common path interferometer for phase-stable cross-sectional acquisition without scanning. Subwavelength variations in surface sample features are measured without interference from spurious reflections by processing the interferometric phase at a selected depth plane, providing a 1.3 nm stability for high signal-to-noise ratio surface features. Nanoscale imaging was demonstrated by measuring the location of receptor sites on a DNA assay biochip and the surface topography of erythrocytes in a blood smear.