There are no sub phases for run_phase. What one should understand is that there is 'run_phase' and the 'run-time phases'. The 'run_phase' is a single phase, while the 'run-time phases' are a group of phases that run sequentially. The 'run_phase' runs in parallel to the 'run-time phases'.
Now why do we need a set of separate 'run-time phases'? It is provided for those who need fine control over the execution of 'run_phase'. These allow us to have a fine control over the running of test; i.e. when the reset should happen e.t.c