This method determines if the phase should be run, based on the
Options object it is passed.
By default, phases are always performed.
Subclasses should override this method if they only want
to be performed conditionally.
This method is called immediately before performPhase. Phases
that do not need to create a new instance for each execution may
override this method to return this, but this must be done
carefully! Classes that don't override this method need to