Phenolic foams (PFs), made from the chemical foaming of phenolic resins after the addition of additives (e.g. hardening agent, foam stabilizer and foaming agent), are polymeric materials with many advantages such as extremely high flame retardancy, low smoke quantity, and self-extinguishing. However, the application of PFs is severely limited by their brittleness and high pulverizability due to their unique molecular structure. To further exploit the desirable properties of PFs, it’s necessary to improve the toughness of PFs and reduce the brittleness and pulverizability. This paper reviewed the main toughening methods of PFs, PFs toughened with polyurethane prepolymer (PUP) (PFs toughened by direct mixing method, PFs toughened with NCO-terminated PUP and OH-terminated PUP) as well as the toughening mechanism was introduced. In addition, the problems of PFs toughened with PUP were summarized.