Thermal conductivities of OCMG-processed (Nd, Eu, Gd)Ba₂Cu₃O_y [NEG123] bulk samples containing 10, 20 and 30mol% second phase [SP:NEG211:(Nd, Eu, Gd)₂BaCuO₅] have been studied between 10-20K, and 100-150K and up to 14T. Thermal conductivity κ of the sample with SP 10mol% shows a clear enhancement below T_c, which is a common feature of high-T_c oxide superconductors. The enhancement becomes smaller as the SP amount increases. The magnitude of the thermal conductivity decreases with the increase in magnetic field, but the magnetic field dependence is very small in all samples. There is a strong correlation between κ(peak)/κ(100K) and the average SP size. It turns out from these results that phonon thermal conductivity is dominated in these samples, and is strongly affected from the scattering by SP.