Telephonic as an adjective is of, pertaining to, or transmitted by telephony while Telecommunication as a noun is the science and technology of the communication or messages over a distance, especially using electric, electronic or electromagnetic impulses
Part of speech: adjective
Definition: Of, pertaining to, or transmitted by telephony
Part of speech: noun
Definition: The science and technology of the communication or messages over a distance, especially using electric, electronic or electromagnetic impulsesA message so transmitted
We hope you now know whether to use Telephonic or Telecommunication in your sentence.