The Phillips County Genealogical Society is still somewhat active, I got some help from Bill Miller, you can reach him at abmiller-at-ruraltel.net (substituting the at sign to avoid email scrapers).
There are a couple books you might find helpful too that they should have at the Phillipsburg library or check in worldcat.org.
Phillips County Epitaphs and Inscriptions - Bill has this and scanned some pages for me, it's a collection of headstone inscriptions from the 57 county cemeteries.
Phillips County, Kansas Early Settlers - a book with profiles of early settlers from the 1800s, a few of my ancestors were in this.
Phillips County Marriages Book A 1873-1886 - I don't think they ever wrote Book B. These last 2 were by the Kansas Historical Society I think.
Hopefully this helps, good luck!