Yealink SIP-T54S Administrator's Manual page 871

Parameter
the parameter "features.speaker_mode.enable" to 1 (Enabled). If you want to user headset
ringer device for the phone, you have to set the value of the parameter
"features.headset_mode.enable" to 1 (Enabled). It is not applicable to CP860/CP920 IP
phones.
Web User Interface:
Features->Audio->Ringer Device for Headset
Phone User Interface:
None
To configure ringer device for headset via web user interface:
Click on Features->Audio.
1.
Select the desired value from the pull-down list of Ringer Device for Headset.
2.
Click Confirm to accept the change.
3.
Configuring Audio Features
Permitted Values Default
845