I think Walker was one of DD mistakes, but he is not awful.
However, from a roster spot value perspective, if you get roughly equivalent performance from Phillips, then Walker with his sizeable salary is worth hanging onto only for as long as it takes to find a decent trade offer.
That is, after all,the main role of the farm - provide talented players at bargain basement cost over multiple years for the ML team. If the farm cannot do that, then the Phillies have a much larger problem, but that still does not mean we continue to sign Walker types and expect miracles.