Turn off Silent Mode
Increase the volume with the side buttons
Open Control Center and raise the volume slider
Go to Settings > Sounds & Haptics and increase Ringer and Alerts
Disable Reduce Loud Sounds in Settings > Sounds & Haptics > Headphone Safety
Turn off EQ in Settings > Music > EQ
Clean the speaker grills
Remove any case or screen protector blocking the speakers
Restart the iPhone
Update iOS
Check for Bluetooth connections and disconnect them
Use mono audio or sound settings if needed
Place the iPhone on a hard surface for better sound projection