I presume this is the Gothaisches Hofkalendar (or the Genealogisches Handbuch des Adels - Genealogical Handbook of the Nobility. Colloquially known as the "Gotha" for its predecessor, the Almanach de Gotha, it attempts a comprehensive listing of all German noble houses (families).
A "Hofkalender" is a printed overview about authorities which is including the names of persons serving for the court, state or military in one of the German states (like Württemberg). The correct name of the wanted person is possibly Philipp Albrecht von Württemberg.
Philipp Albrecht Herzog von Wuerttemberg was an Oberleutnant and retired as a Major. (If we are talking about the same man.) Source: "Ehren-Rangliste des ehemaligen Deutschen Heeres", E.S. Mittler and Sohn, Berlin, 1926. However, there were other Philipp's and Albrecht's, but only one Philipp Albrecht.
Was this rank in the Prussian Army? I am told that a Royal can hold a Prussian Army rank yet have a much higher rank in the kingdom, duchy, or state to which they are in the royal line.
Only one other that I know of: Philipp Herzog von Wuerttemberg. He was, indeed, a Gen.Oberst. He was also KIA on 11Oct17. Ulanen-Regiment Koenig Karl (1. Wuerrtembergisches) N. 19.