Two kinds of phenolic resin, novolak and resets, have been studied with an addition of cobalt at pressures between 2 and 4 GPa and at temperatures from 1300 to 1900 degrees C, all under thermodynamically graphite-stable conditions. Diamond was synthesized from these resins which had been pre-fired at 500-1000 degrees C. From such resins, carbon precursors carrying a great number of radicals, being nearly free of hydrogen and oxygen, and turbostratic in structure, can be constructed. The pressure-temperature conditions suitable for the diamond synthesis were dependent on the pre-firing temperatures. The cobalt served as a catalyst-solvent, similar to the case of conventional diamond synthesis from graphite under diamond-stable conditions. Well-defined single crystals cube-octahedral in shape, measuring 0.3-0.7 mm across and classified as type Ib were obtained.