LG G5300 User Manual page 196

You can connect a call on hold to the currently active call to form a
multiparty call by selecting the [Options] key then
.
To put a multiparty call on hold, select the [Options] key then
.
To de-activate a multiparty call on hold, select the [Options] key then
To join an active call to the held multiparty call, select the [Options]
key then .
To scroll through the numbers of the callers who make up a
multiparty call on the handset screen, press U and D keys.
To place one selected caller (whose number is currently displayed
on-screen) of a multiparty call on hold, select the [Options] key then
.
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