Walker is definitely helped by the fact that the Phillies did not bring in much competition for him. The first 7 bullpen spots seem set absent injury:
LH: Alvarado, Strahm, Banks
RH: Romano, Kerkering, Ross, Ruiz
That leaves Walker competing with Lazar, Phillips, Mercado, Rangel and a cast of unknowns (Vespi, Sweet, McMillon) for the last spot. Lazar has options and probably does need more AAA time. Rangel is intriguing but more as a starter (like Phillips). McMillon throws 100 but not necessarily in the strike zone and has options. The NRI pitchers without options are not good enough to throw away an arm like Walker now.
So there is really no option other than to give Walker the last spot and see how it goes. There is more need for long relief in April as well. Once we get to May is when the Phillies really need to decide if Walker helps or hurts.