Differential x-ray phase contrast imaging using a grating interferometer was combined with a magnifying cone beam geometry using a conventional microfocus x-ray tube. This brings the advantages of a magnifying cone beam setup, namely, a high spatial resolution in the micron range and the possibility of using an efficient, low resolution detector, into differential phase contrast imaging. The authors present methodical investigations which show how the primary measurement signal depends on the magnification factor. As an illustration of the potential of this quantitative imaging technique, a high-resolution x-ray phase contrast tomography of an insect is presented.