Digestion of cellulosic biomass solids can be enhanced in the presence of a phenolic solvent. Methods for digesting cellulosic biomass solids can comprise providing cellulosic biomass solids containing up to about 50% water by mass in a digestion medium comprising about 50% or more of an organic solvent by volume; heating the cellulosic biomass solids and the digestion medium in a digestion unit in the presence of molecular hydrogen and a slurry catalyst capable of activating molecular hydrogen, thereby forming an alcoholic component derived from the cellulosic biomass solids and liberating lignin therefrom; wherein the digestion medium and the water form a biphasic mixture in which the alcoholic component, slurry catalyst, and lignin are contained; removing at least a portion of the biphasic mixture from the digestion unit; converting at least a portion of the lignin into a phenolic solvent; and returning the phenolic solvent to the digestion unit.