noun
main switchboard number; central phone line
Refers to the primary phone number for an organization, used to reach a receptionist or operator who can connect callers to the appropriate extension.
会社の代表電話にかけて、担当者につないでもらった。
I called the company's main switchboard and was connected to the person in charge.
内線 is an extension line within an organization, while 代表電話 is the main external number that connects to the switchboard.
Compound of 代表 (representative) and 電話 (telephone), literally 'representative telephone'.