Phthalates are harmful to human health. The purpose of this study was to determine dust-phase phthalate levels in 112 dormitories of 14 universities during autumn and winter, analyze the seasonal variation of phthalates, and investigate the potential sources of phthalates in the two seasons. Twelve phthalates were detected, among which di-isobutyl phthalate (DiBP), di-n-butyl phthalate (DnBP), di-(2-ethylhexyl) phthalate (DEHP), and dicyclohexyl phthalate (DCHP) were the most abundant. The median concentrations of DiBP, DnBP, DEHP, and DCHP were one to two orders of magnitude higher than those of other phthalates. The median concentrations and contributions of DCHP and DEHP were the highest. The contributions of di-n-octyl phthalate (DnOP) and di-nonyl phthalate (DNP) were significantly higher in winter than in autumn. Moreover, phthalate concentrations showed no significant differences between autumn and winter. The potential sources of certain phthalates were iron furniture, chemical fiber textiles, clothes, and personal care products. Medium-density fiberboard (MDF) furniture is probably a sink for phthalates. Our results provide an in-depth understanding of dust-phase phthalates and their potential sources in university dormitory environments.