Headphones for an iPhone are similar to speakers that are used with a stereo system, which require using the receiver to adjust the volume. This means the volume for the headphones is controlled by using settings on the iPhone. To make the headphones louder, you will need to set various options using the iPhone and iTunes.
Insert the small end of the headphones into the stereo headset jack on the iPhone.
Press the "Volume Up" button to turn up the volume on the headphones.
Press the "Volume Down" button to turn down the volume on the headphones.
Repeat this process when you want to use the headphones with the iPhone.
Go to the Music option for your iPhone.
Tap the option for "iPod" and then select "Volume Limit."
Adjust the slider bar to the setting you want for the maximum volume.
Tap the "Lock Volume" option to prevent any changes to the volume level.
Double-click the iTunes icon on your desktop.
Click the "Edit" drop-down and select the option for "Preferences."
Put a check in the box to the left of the "Sound Check" option.
Click the "OK" button to save the change.
The volume-limit option only works when the headphones are connected to the iPhone.