The internal earpiece (top speaker) allows you to hear the person you are talking to. It needs to be replaced on the Samsung Z Flip 4 / Z Flip 5 / Z Flip 6 if it crackles or no longer emits any sound.
This internal earpiece (top speaker) generates the sound of the person you are talking to during a call.
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.