telephone exchange vs phone system

telephone exchange and phone system both are nouns.

Word	Noun	Adjective	Verb	Adverb
telephone exchange	Yes	No	No	No
phone system	Yes	No	No	No

telephone exchange (noun)	phone system (noun)
a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication	a communication system that transmits sound between distant points