Note that the default value for SPECIES_EQ keyword is True, so it should be in effect for solids phase 2 even if not explicitly set in the input file. However it’s still a bit inconsistent that the value is listed for phases 0 (fluid) and 1 but not phase 2.
mfix/model/init_namelist.f
261 !<keyword dtype="LOGICAL" category="Run Control" required="false" locked="true">
d="true">
262 ! <description>Solve species transport equations.</description>
263 ! <arg index="1" id="Phase" min="0" max="DIM_M"/>
264 ! <valid value=".TRUE." note="Solve species equations."/>
265 ! <valid value=".FALSE." note="Do not solve species equations."/>
266 SPECIES_EQ(:DIM_M) = .TRUE.
267 !</keyword>
268