This is a routine masked hero to the rescue serial, the sort that was turned out in the 30s, 40s & 50s by Republic Pictures, masters of the cliffhanger.
In this one, The Phantom Rider of the title is a legendary Indian god who intervenes when Indian tribes are being wronged.
The plot is basically the crooked Indian Agent (LeRoy Mason) trying to prevent the establishment of an Indian Police force for their reservation. This would bring an end to Mason's raiding and robbing of stagecoaches and freight wagons on the reservation.
The hero is Robert Kent who plays a crusading doctor who takes on the role of the Phantom Rider to aid the local Indian tribe in their fight against the evil forces of the afore-mentioned crooked Indian agent. Over 12 chapters we are treated to the usual array of cliff hanging situations, wagon chases, explosions, narrow escapes et al.
As in most Republic serials the cast is competent and the stuntwork is excellent. Serial veteran Peggy Stewart plays the heroine, a (what else?) schoolmarm. George J. Lewis and Chief Thundercloud are the good Indians and Tom London (looking ridiculous in Indian make-up) is the bad Indian. In addition to Leroy Mason, his chief henchman is the veteran Kenne Duncan and there is the usual endless supply of gang members for the heroes to shoot. Rounding out the cast is the venerable Hal Taliaferro in the comic relief role as "Nugget".
Curiously, Roy Barcroft (usually the main villain) and future series star, Monte Hale are listed in the supporting cast, but only appear in Chapter 1.
The Phantom Rider, though not a great serial, is still a cut above most turned out by other studios due to the expertise available at the Republic studio. If you are a serial buff, it's worth a look.