Lower level prospects have less value right now b/c of the uncertainty whether there will be minor league baseball next year, and how many levels.If you lose a team or two it'll be hard to find work for all your marginal pitching prospects.
Plus we don't know how many "futures" the Phillies have signed but won't announce until next year.
Given Klentak's focus on older RP arms, I think they have probably prioritized potential starters in the low minors, and will consider the other arms expendable.