I looked each port for the specific Sphinx's version it requires.
Remaining ports:
audio/ncmpc/Makefile:MANPAGES_BUILD_DEPENDS= ${PY_SPHINX}
audio/aubio/Makefile:DOCS_BUILD_DEPENDS= ${PY_SPHINX}
audio/musicpc/Makefile:DOCS_BUILD_DEPENDS= ${PY_SPHINX}
graphics/zathura/Makefile:BUILD_DEPENDS= ${PY_SPHINX} \
security/libscep/Makefile: ${PY_SPHINX}
lang/pocl/Makefile:DOCS_BUILD_DEPENDS= ${PY_SPHINX}
devel/gearmand/Makefile:BUILD_DEPENDS= ${PY_SPHINX}
devel/gearmand-devel/Makefile: ${PY_SPHINX}
sysutils/zrepl/Makefile:MANPAGES_BUILD_DEPENDS= ${PY_SPHINX}
net/savvycan/Makefile:BUILD_DEPENDS= ${PY_SPHINX}
net/frr7/Makefile:MANPAGES_BUILD_DEPENDS= ${PY_SPHINX}