Pretty much straight north of the later and permanent Ft Arbuckle. The distance sounds about right (50 miles or so). It was the first post built by Capt Marcy (1850?) but abandoned for the better location on Wild Horse Creek.
Like I said, it's possible Phillips was there (i.e., Old Ft Arbuckle) in person but it seems unlikely to me. I'm skeptical but open to more evidence. The name "Little River Town" would suggest a place near Little River and Old Ft Arbuckle is not near Little River -- its on the south side of the Canadian. Old Ft Arbuckle doesn't fit with Phillips statements that he retraced his route back to Ft Gibson.