I see what you're saying from the on the field point of view.
However, I'd argue that Brandon Phillips is the face of this franchise, even moreso than Joey Votto. He's exciting, personable and marketable. The fans love him, adults and kids alike. Baseball is a sport, but also a business, and you not only have to factor in winning to bring fans to the ballpark, but also players that the fans want to come and see. Right now, that person that the fans want to come and see in Cincinnati is Brandon Phillips. He wants to be here. The fans want him here. You figure out a way to make that happen.
Also, he's won two gold gloves. I think a case could be made that he's the best second baseman the Reds have had since Joe Morgan. That's a long stretch. He's won two gold gloves. Even if he begins to decline defensively, I think the chances of him still being better than any potential replacement are great.