통화가 · 통화를
phone call, phone conversation
Example
지금 통화 중이니까 잠깐만 기다려 주세요.
I'm on a call right now, so please wait a moment.
Word parts
통 pass through+화 talk
Literally 'talk passing through' the line.
Good to know
Watch out: 통화 'phone call' sounds the same as 통화 'currency'.