From Wiki:
"A photograph in The Louisiana Weekly of January 14, 1928 shows Phillips holding two fretless zither-like instruments. That date lies between the second and third of his five recording sessions. The instrument in his right hand has been identified as a celestaphone and that in his left as a phonoharp, both manufactured by the Phonoharp Company; in both cases with the hammer attachment missing (the instruments as sold were a type of hammered dulcimer).[4]
In the 1960s, Frank B. Walker identified Phillips’ instrument to musicologist and author Paul Oliver as a “dulceola”, saying that “nobody else on earth could use it except him”. Before a recording session, Phillips would spend half an hour or more assembling it.[1] It has often been assumed that Walker meant a dolceola, but that cannot be so: the dolceola was manufactured, sold, and recorded commercially, and did not need assembly before use. It seems more likely that the name “dulceola” was coined specifically for unusual instruments made by Phillips himself from broken discarded ones.
The aural evidence suggests Phillips strummed and plucked the strings of his instrument, and did not hammer them. Some listeners have claimed to discern differences between the instruments he used in different songs.[5]"
I think it makes a magical sound whatever it is!