phrosty performs difference-imaging forced photometry for Type Ia supernovae in simulated Nancy Grace Roman Space Telescope data. It takes sequences of Roman images divided into template and science exposures, subtracts the templates from the science images using SFFT-based image subtraction, and measures point-source flux at specified sky positions on each difference image to build light curves at the science-image MJDs. The code operates on OpenUniverse Roman simulations in FITS format, using the WCS information in the headers for image alignment, and obtains point spread functions from galsim (ascl:1402.009) and a specific version of the roman_imsim package for both PSF photometry and PSF matching. phrosty integrates a GPU- and CPU-based implementation of the saccadic fast Fourier transform (SFFT) method to handle Roman’s spatially varying PSF and the large data volume expected from the High Latitude Time Domain Survey. Running in a Roman SN PIT environment with SFFT and roman_imsim, it produces difference images, associated PSF and auxiliary products, and forced-photometry light curves for Roman supernova analyses.