phototelegraph vs telegraphy

phototelegraph and telegraphy both are nouns.

Word	Noun	Adjective	Verb	Adverb
phototelegraph	Yes	No	No	No
telegraphy	Yes	No	No	No

As nouns, telegraphy is a hypernym of phototelegraph; that is, telegraphy is a word with a broader meaning than phototelegraph:

phototelegraph: an apparatus for transmitting pictures by phototelegraphy.
telegraphy: apparatus used to communicate at a distance over a wire (usually in Morse code)

Other hypernyms of phototelegraph include telegraph.

phototelegraph (noun)	telegraphy (noun)
an apparatus for transmitting pictures by phototelegraphy.	apparatus used to communicate at a distance over a wire (usually in Morse code)
	communicating at a distance by electric transmission over wire