iPhone speaker volume in general has been a long standing issue with me. I had a Motorola Q that by comparison, would almost "wake the dead" when it rang. I found a ringtone creating program, that runs on my PC, called "iRinger" that will allow you to create custom ringtones and can also increase that ringtone's volume maybe 30%-40%. It is a little cumbersome to use and will require some experimentation to get it right but it's free and it works. I used a ringtone similar to the one on the iPhone called "old phone" and boosted the volume on it and when playing the two one after the other on my phone, there is a definite increase in volume with the one I created. unfortunately, you are limited by the iPhone's low audio output power but every little bit helps.