Some cars leave a paper trail; the Rolls-Royce Phantom I sedan left a name, a year — 1928 — and a place in Rolls-Royce's list. What follows is what can be said with a source behind it.
Its place in the line
The cars a buyer would have weighed it against include the Mercedes-Benz W06, the DKW Typ P, the Mercedes-Benz W08. Nearby in the Rolls-Royce catalogue sit the Rolls-Royce 100EX and the Rolls-Royce 102EX.
Owning one today
MotorJury scores cars on the United States complaint and recall record, and the Rolls-Royce Phantom I sedan has none: too old, too rare, or never sold there. Its value today is a collector's question, decided by provenance and condition rather than by a class average.
The record
The open record for the Rolls-Royce Phantom I sedan carries no verified engine, output, weight or price yet. MotorJury does not fill gaps with guesses; this entry gives the model a home in the catalogue and grows as sourced specifications and photographs arrive. Corrections: corrections@motorjury.com.
Rolls-Royce Phantom 
Rolls-Royce Phantom I