This coin came from the same lot as the other two that I just posted: Is it my imagination, or does the obverse portrait look suspiciously like Gordian III? Initially I thought this was Philip II, but every other example that I was able to track down lists it as Philip I. I don't know a lot about these coins from Antioch in Pisidia, but if I had to guess, I'd say this was minted very early in Philip's reign, before the celators at Antioch knew what he looked like. Philip I ("the Arab"), A.D. 244-249 AE27 PISIDIA, Antioch Obv: IMP [M] IVL PHILIPPVS P F AVG P M - Radiate bust of Gordian III, pretending to be Philip I, the man who assassinated him. Rev: CAES ANTIOCH COL - Tyche, turretted, standing, facing left, holding downward-pointing baton in right hand and upright spear in left; globe at feet, all between S and R. Mionnet 89 27 mm, 12.1g BTW, does anyone know what the SR stands for?
From Numiswiki: S. R. appears on the field of certain coins, about the time of Constantine, signifying Salus Romanorum or Spes Reipublicae. S. R. Senatus Romanus.-- On coins of Antioch in Pisidia, instead of S. C. Senatus Consulto. Obviously, the second applies to your coin.
Thanks, @DonnaML. So I guess we can assume that the Roman Senate guaranteed the value of these coins. I didn't know this.
The letters S R begin to appear on the coins during the reign of Septimius Severus. At first they occurred only on coins of sestertius size, but they appear during the reign of Gordian III on smaller size, and from that time, on all the coins alike. These letters reflect the title of Socia Romanorum, the Latin translation of the Greek σύμμαχος Ῥωμαίων, meaning "ally of the Romans." This embodied the notion of Antioch's status as an independent city with continued loyalty to Rome during a century of increasing military pressure on the empire. In material terms, this meant the city sent recruits, provisions, and equipment to the armies on the eastern frontier. See Mitchell, Stephen, et al. Pisidian Antioch: the Site and Its Monuments. Duckworth, 1998, p. 11.