Option #3: Move Alec Bohm to first base
Alec Bohm played most of the first base for Philadelphia this season out of necessity. Darick Hall, Jake Cave, and Kody Clemens simply weren't getting it done at first base, and the Phillies needed more. Using Bohm at first base and Edmundo Sosa at third gave the Phillies the best chance to win for a while before Harper got settled at first and before Johan Rojas was brought up for the first time.
Bohm showed a lot of strides at third base this season, particularly in the postseason. It felt like Bohm made most of the plays defensively at the hot corner, even when his bat was lagging. Even with that improved defense, it's not an impossibility Philadelphia decides to move him across the diamond. After all, there's a very real chance that first base might be Bohm's best spot defensively.
Still, it's unlikely, as it'd require the team to bring in a third baseman. Sosa's serviceable, but he's not good enough against righties offensively to play every day. If Philadelphia had interest in one of the third baseman free agents and wanted to move Bohm over to first, it wouldn't be the most shocking thing in the world.
If they did that, Harper would be moved back out to the outfield, and Johan Rojas would revert to a bench role. The Phillies would take a step back defensively in the outfield but could arguably take a step forward in the infield, depending on who they bring in to play third base.