The biological species concept looks at the things, like reproductive isolation, which lead species to form evolutionary mechanisms. The phylogenetic species concept, instead, looks at the patterns/relationships among species. Neither concept is the right one always, and both have instances where it is easier to apply than the other and instances where it is harder. Both are valuable tools for seeing evolutionary relationships.
Work Step by Step
First, define these two concepts and relate them to mechanism (try listing some from Ch. 22) and pattern (list from this chapter). Both are tools with no obvious superiority in all cases, so both must be true in some cases.