I find this interesting as it is the only developer I know of other than POTA using only Phenidone as a developing agent. The patent by Kendall (U.S. Pat. 2,289,367) is from 1942. My source for the formula is Modern Photographic Processing by...

A concentrated, Phenidone-only developer (J. D. Kendall)
A concentrated, Phenidone-only developer (J. D. Kendall)