The thermal diffusivity α and conductivity κ of YBa2Cu3O7—δ sintered crystals with oxygen deficiencies δ ≈︂ 0.10 (90 K-phase) and δ ≈︂ 0.35 (60 K-phase) have been quasi-simultaneously measured between 15 and 170 K. The phonon and electron components of α and κ are separated and analyzed from viewpoints of both the d- and s-wave superconducting energy gap models. It is found that the enhancement of κ below Tc, which is commonly observed for 90 K- and 60 K-phase YBa2Cu3O7—δ, is consistent only with the phonon origin model under d-wave energy gap anisotropy with the maximum gap 2Δmax/kBTc ≈︂ 5. The phonon scattering mechanisms are synthetically analyzed for both 90 K- and 60 K-phase YBa2Cu3O7—δ and the oxygen vacancy is found to be one of the dominant phonon scattering centers in this system.