LG G5200 User Manual page 213

You can make a second call while you are already in a call. To do
this, enter the second number and press [Send]. When you get
second call the first call is automatically put on hold. You can swap
between calls by selecting the [Menu] key then .
You can connect a call on hold to the currently active call to form a
multiparty call by selecting the [Menu] key then
l.
To put a multiparty call on hold, select the [Menu] key then
.
To make a multiparty call on hold active, select the [Menu] key
then .
To join an active call to the held multiparty call, select the
[Menu] key then .
To scroll though the numbers of the callers who make up a multiparty
call on the handset screen, press and keys.
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