Placing A Call On Hold

TL;DR

To place a call on hold, press the pause button on the phone. This puts the caller on a temporary hold that can only be retrieved from your phone. To pick up the call again, press the blinking green line button on your phone. This type of hold does not allow other extensions to answer the call.

To place a call on hold, press the pause button on the phone.
To pick up the call again, press the blinking green line button on your phone.

Placing a caller on hold, puts the caller on a temporary hold on your phone, it does not allow someone from another extension to answer the call, to place someone on a hold that would allow another extension to pick up, see Parking a Call.