The conference call function on your OnePlus 8 5G UW lets you talk with multiple people simultaneously so up to 6 parties can participate in the same conversation.
Do one of the following:
From the Keypad, enter a 10-digit number then tap the
Dial icon

.
From the Contacts tab, select a contact then tap the
Call icon

.
Once the call is connected, tap
Add call
.
Each call must be initiated by the call originator.
If RTT is enabled, tap the Menu icon

then tap
Add call
.
Do one of the following:
Enter a 10-digit number then tap the
Dial icon
.
From the Contacts tab, select a contact then tap the
Call icon
.
Once the call is connected, tap
Merge.
To disconnect from either party, tap the
down arrow

then tap
Drop
(to the right of the corresponding call).