If your iPhone alarm is too quiet, the most important setting is the alert volume rather than the volume used for music and videos. You can raise it in Settings and then test the alarm before relying on it.
- Open Settings and tap Sounds & Haptics.
- Under Ringtone and Alerts, drag the volume slider to the right.
- If you do not want the side volume buttons changing the alarm volume accidentally, turn off Change with Buttons.
- Open the Clock app, tap Alarms, and edit the alarm you use.
- Tap Sound and choose an alarm tone that is easy for you to hear, then save the alarm.
An alarm can also seem quiet if its selected sound is gentle or if the speaker is obstructed. Test the alarm while you are awake. If you use the Sleep/Wake Up alarm, its volume can have a separate control in the sleep schedule settings.