  The photospheric emission in the prompt phase is the natural prediction of
the original fireball model for gamma-ray burst (GRB) due to the large optical
depth ($\tau >1$) at the base of the outflow, which is supported by the
quasi-thermal components detected in several Fermi GRBs. However, which
radiation mechanism (photosphere or synchrotron) dominates in most GRB spectra
is still under hot debate. The shape of the observed photosphere spectrum from
a pure hot fireball or a pure Poynting-flux-dominated outflow has been
investigated before. In this work, we further study the photosphere spectrum
from a hybrid outflow containing both a thermal component and a magnetic
component with moderate magnetization ($\sigma_{0}=L_{P}/L_{\text{Th}}\sim
1-10$), by invoking the probability photosphere model. The high-energy spectrum
from such a hybrid outflow is a power law rather than an exponential cutoff,
which is compatible with the observed Band function in large amounts of GRBs.
Also, the distribution of the low-energy indices (corresponding to the
peak-flux spectra) is found to be quite consistent with the statistical result
for the peak-flux spectra of GRBs best-fitted by the Band function, with
similar angular profiles of structured jet in our previous works. Finally, the
observed distribution of the high-energy indices can be well understood after
considering the different magnetic acceleration (due to magnetic reconnection
and kink instability) and the angular profiles of dimensionless entropy with
the narrower core.
