Phase-change　materials　(PCMs)　provide　an　alternative　avenue　for　modulating　the　adjacent　layer　property　through　interfacial　effect,　which　sometimes　is　more　effective　than　the　traditional　methods.　Here,　a　systematic　study　of　the　phase-change　induced　control　of　FMR　resonance　field　in　Si/GeSbTe/FeCoB　heterostructures　is　presented.　We　show　that　different　crystalline　phases　induced　by　thermal　anneal　in　GeSbTe/FeCoB　films　contribute　to　large　shifts　in　resonance　field　of　FeCoB　up　to　15　mT.　The　correlation　between　GeSbTe　phase　change　and　anisotropic　field　of　FeCoB　is　confirmed　from　the　GeSbTe　film　morphology　dependent　of　stress.　These　results　propose　a　method　of　phase-change　induced　control　of　FMR　resonant　field　and　ferromagnetism　in　PCM/ferromagnetic　alloy　film　heterostructures　by　controlling　interface　roughness,　which　can　be　introduced　in　the　optimization　of　ferromagnetic　alloy　film　parameters　and　development　of　high　functioning　magnetic　devices.