  We present an update on the study of the QCD phase transition with 3 flavors
of M\"obius domain wall fermions at zero baryon density. We performed
simulations on lattices of size $36^3\times12\times16$ and
$24^3\times12\times32$ with a variety of quark masses at a fixed lattice
spacing $a=0.1361(20)$ fm, which correspond to a temperature 121(2) MeV. By
analyzing the chiral condensate, chiral susceptibilitities and Binder cumulant
on $36^3\times12\times16$ lattices together with the result obtained from our
previous study on $24^3\times12\times16$ lattices, we identified a crossover
occurring at quark mass around $m_q^{\mathrm{\overline {MS}}}(2\, \mathrm{GeV})
\sim 3-4$ MeV for this temperature. Besides, we show the effects of residual
chiral symmetry breaking on chiral condensate and chiral susceptibilities
between $L_s=16$ and 32.
