  We have investigated the electronic properties of
SrFe$_2$(As$_{1-x}$P$_x$)$_2$ ($0\leqq x\leqq1$) single crystals with
postannealing treatment and established a phase diagram of this system. The
postannealing treatment reduced the residual resistivity in an
antiferromagnetic-orthorhombic phase and enhanced the superconducting
transition temperature to $T_{c, optimal}$=33\,K in the superconducting phase.
The obtained phase diagram and electronic properties are similar to those of
BaFe$_2$(As$_{1-x}$P$_x$)$_2$ despite the large difference in lattice
constants. This indicates that, for superconductivity, the dimensionality of
the Fermi surface determined by the crystal structural anisotropy is less
important than the pnictogen height from the Fe plane.
