Rich Eisen pointed out that if the Eagles and Lions end up tied for the #1 seed, the first tiebreaker is not conference record but rather record against common opponents: KC, Seattle, Tampa, Dallas and Minnesota. The Lions and Eagles have both beaten Tampa already, so that's a wash. The Lions have defeated KC and lost to Seattle, the Eagles' will play KC and Seattle on December 17. The Eagles already have a win against Minnesota and a win against Dallas. So by count, the Lions are 2-1 with 3 games left (2x Minnesota, Dallas) while the Eagles are 3-0 with with 3 games left (KC, Seattle, Dallas).
Lions-Niners common opponents in 2023 are Dallas, Minnesota, Tampa, Seattle and Baltimore.
EDIT: Eisen might be wrong. From NFL.com. The Eagles conference record is 6-0 and still will be after tonight's game, while the Lions and SF are both at 5-1.
Two Clubs
Head-to-head, if applicable.
Best won-lost-tied percentage in games played within the conference.
Best won-lost-tied percentage in common games, minimum of four.
Strength of victory.
Strength of schedule.
Best combined ranking among conference teams in points scored and points allowed.