Phrases.com is a great domain, if you developed it. You could have a great site with FB plugins, email subscription, etc and its own social network. You can easily buy a dbase of famous quotes to base it on. Basic access would have to be free but you could offer mugs, tshirts etc with any phrase printed (Cafepress.com).
Anyway, what crosses my mind first is, why would a FB app even need a domain like this? If they are
#1 on FB, they dont need anything. FB app success might be something like the situation with domains and top movies - the movie makers dont really care about domains. The movie makes it or not, and its success later in DVD and streaming is not based on a domain. You cant sell a domain to a movie studio for big money, just not going to happen. Is this going to be the case with FB top apps?
Apps peak and then settle down, which is also like movies. However: just as farmville has lost its
#1 spot, eventually Phrases will lose its
#1 spot on FB. So maybe your best potential customer is the owner of the FB app? Or perhaps you approach Farmville. That is what I would do. Why cant farmville create a Phrases app, add some gaming elements to it. expand their offerings, and thereby compete with the Phrases app. If that was your plan you might get a higher price by doing some initial dev first.
You could also pitch it to dictionary.com and any large dictionary/encyclo publisher. The success of the FB app should be used to your advantage as you pitch it, for sure.
Kevin