Functionalized graphene modified by silane coupling agents was added to phenolic resin to prepare phenolic resin composites, and the effects on the flame retardancy, thermal properties, and mechanical properties of the composites were investigated. The results showed that the phenolic resin composite with a 30% mass fraction of functionalized graphene had a limiting oxygen index (LOI) of 46.6% and an UL-94 rating of V-0. The tensile strength and flexural strength of the material were increased by 34.42% and 13.27% respectively compared with pure phenolic resin. At the same time, the thermal stability was also effectively enhanced.