The telephone rings. The caller appears on the screen. 

Press the key. The LED lights up.
Speakerphone mode. 

Raise or lower the volume. Keep pressing the key until the desired volume is set. 

Ending the call:

Press the key. The LED goes out. 

Press the key. 

Notes on speakerphone mode:

Tell the other party that you are using speakerphone mode.

The speakerphone works bests at a low receiving volume.

The ideal distance between the user and the telephone set in speakerphone mode is about 50 cm (approx. 20 inches).