Set the ringtone, alarm bell, voice call and media volume to the highest level in the mobile phone settings, and then try them one by one to see which part is wrong.
when making a phone call, turn the volume button on the outside of the phone to the highest level. If the sound is still low, it may be that the receiver of the mobile phone is broken.
if you play a song on speakerphone and your mobile phone, the speaker may be broken.
if people can't hear me on the phone, it may be that the microphone of the mobile phone is broken.
software conflict, which may be caused by the volume reduction of your mobile phone due to the third-party software you recently downloaded. Uninstall the recently installed software, and then restart the phone.