Like many people, I have also had problems with the iPhones ringtone volume. In order for this to work you have to be able to make your own ringtones. There are many tutorials on this site and on YouTube that show you how to do it. After you have made the song the appropriate length, you can increase the volume of the track under the "Mixer" section of GarageBand. After you increase the volume (make sure not to increase it too much or the song sounds bad) you need to save the track and send it to iTunes, then continue making your ringtone as you normally would. This made a difference for me and I hope it works for everyone else.