The external speaker (bottom speaker) allows you to hear the person you are talking to in speakerphone mode. It needs to be replaced on the Samsung S21 Ultra if it crackles or no longer emits any sound.
This external speaker (bottom speaker) generates the ringtone when you receive a call or notification.
Here are some signs that indicate it needs to be replaced:
Replacement is very simple and takes about 15 minutes; no repair knowledge is necessary.