Increase the ringer and alert volume in Settings > Sounds & Haptics
Turn off Change with Buttons if you want the volume to stay high
Set your alarm sound to a louder tone in the Clock app
Avoid using “None” or very soft alarm sounds
Turn off Sleep Focus or Do Not Disturb if it may silence alerts
Make sure the alarm volume is not lowered by Bluetooth headphones or speakers
Disconnect Bluetooth devices before sleeping
Place the iPhone on a hard surface to help the sound carry
Clean the speaker openings if sound seems muffled
Update iOS if alarm or sound issues continue
Restart the iPhone if the alarm volume still seems low