Call up and Get on the line

Call up verb - Get or try to get into communication (with someone) by telephone.

Get on the line and call up are semantically related in telephone topic. In some cases you can use "Get on the line" instead a verb "Call up", when it comes to topics like communicate through telephone system.

Call up and get on the line are semantically related in telephone topic. You can use "Call up" instead a verb phrase "Get on the line", if it concerns topics such as communicate through telephone system.