Interesting question.

I agree with Sandy; if Mrs. Phillips was as sensible as her brother the Bennet's girls would likely be somewhat different. Jane and Elizabeth would have another relative of action and sense. Rather than yelling out the window to invite Wickham and co. into her home, a more sensible woman would have kept quiet and admonished her neices for their forward behavior when they came inside. Then again, Lydia may be less inclined to visit her aunt if she had more rules!

Mrs. Bennet would likely still be the silly Mrs. Bennet but with one less conspirator in her ridiculousness. A sensible Mrs. Phillips would have done her best to keep her sister and the rest of the household quiet about Lydia's elopement (if she was still inclined to do so) rather than wailing with her sister.