An imaging system with on-chip phase-detection includes an image sensor with symmetric multi-pixel phase-difference detectors. Each symmetric multi-pixel phase-difference detector includes (a) a plurality of pixels forming an array and each having a respective color filter thereon, each color filter having a transmission spectrum and (b) a microlens at least partially above each of the plurality of pixels and having an optical axis intersecting the array. The array, by virtue of each transmission spectrum, has reflection symmetry with respect to both (a) a first plane that includes the optical axis and (b) a second plane that is orthogonal to the first plane. The imaging system includes a phase-detection row pair, which includes a plurality of symmetric multi-pixel phase-difference detectors in a pair of adjacent pixel rows and a pair, and an analogous phase-detection column pair.