To me right now it's Maton vs. Hall. And Maton was actually better.
0.6 WAR, .341 OBP, .514 SLG, 138 OPS+, 5 HRs in 72 ABs
0.4 WAR, .282 OBP, .522 SLG, 121 OPS+, 9 HRs in 136 ABs
SSS/likely not sustainable, but you can say the same about Hall, what he did wasn't actualy that impressive and he would likely be exposed further (and the Phillies obviously knew it too).
Put Maton in RF against RHP with Vierling on the other days and just let Castellanos DH. And either of them can also spell Schwarber (or Hoskins). And Maton could also play 3B against RHPs if they don't want Sosa some days.
By all means, they can bring in competition for both Maton and Vierling in spring training, but they don't want to spend too much $ and the players who would cost $ probably don't want the job (since they'd be benched or traded once Harper came back).
I just don't think they are trying to platoon Stott. Or Marsh for that matter. And not Bohm either. Sosa will just get his 1-2 starts moving around, though if he's as good as the Phillies hope he is they'll also consider trading him in the end.