The Phillies are probably better with Harper at 1B but the improvement might not be from giving Sosa and Harrison less time. It might be in getting Schwarber and/or Castellanos out of the outfield. The Dodger series alone had 5+ outfield balls that might have been caught by a Jake Cave (and later we could be playing Pache and/or Muzziotti out there next to Marsh).
Sosa has been good. I think he is still getting used to 3B but it is not as if he has been worse than Bohm. It is a crude measure but RF/9 is 2.43 to 1.61. Bohm catches what he gets to but does not get to much. Sosa will decrease the errors over time as he has much more experience in the middle infield. At the plate though neither offers the offense one should get at 1B. So defensive improvement (in the outfield) is the advantage we get from playing Harper at 1B.
A different question might be whether we are better with Hall at 1B once he is back. Slightly better defense at 1B than Harper, but it costs us that DH defense benefit in the outfield. Is Hall at 1B and Harper at DH better than Harper at 1B and Cave/Muzziotti/Pache/Sosa/Harrison in LF.