Harry has a brogue in this one to rival Barry Fitzgerald. He married a Mexican woman and his niece by marriage Carla Balenda is his heir. He also has an adopted minor child Peter Price who is the son of his housekeeper Rosa Turich. If this were not a western that was aimed at a juvenile audience, the script would have been more frank about Price's origins.
In any event Balenda and boyfriend Don Haggerty who is the foreman have been stealing horses and selling them and blaming the loss on a wild stallion. Then they try murder and succeed in blaming the stallion for killing Shannon. Of course Rex and Slim get to the bottom of everything in the fashion of the B westerns of the time.
The B western was winding down at this time, something that Herbert J. Yates of Republic did not foresee. Items like Phantom Stallion were being done on television now and Rex Allen was the last of Yates's stable of cowboy stars and in a year he would leave the studio also.
Still the stories and the productions of these were at their best at the end and Phantom Stallion is a good film with no phantoms, but lots of live action.