I would understand a central phantom. The word-order puzzles me. Does phantom central have a specific meaning? Is central a postpositive adjective there? Thanks in advance :).
And now a madcap humour came upon me. It was plain Bellairs had been communicating with his principal; I knew the number, if not the name. Should I ring up at once? It was more than likely he would return in person to the telephone. Why should not I dash(vocally) into the presence of this mysterious person, and have some fun for my money? I pressed the bell. "Central," said I, "connect again 2241 and 584 B." A phantom central repeated the number; there was a pause, and then "Two two four one," came in a tiny voice into my ear - a voice with the English sing-song - the voice plainly of a gentleman.
(The Wrecker by R. L. Stevenson and L. Osbourne, chapter x)
There is another thing that puzzles me. The text says there is the telephone number 584 B. Were there letter-dials in addition to the number-dial in America in former times?