How do you boost your iPhone volume? By grouping a bunch of iPhones together and using Seedio. It's a new app that solves the problem of increasing the volume, and it does so by turning several iPhones into one large speaker.
To use Seedio, you'll need to install the app on every iOS device you want to turn into a speaker. Set up one of the devices as athe hot spot by adding a list of songs and then every other device receives the music from the original.
Every iOS you have connected is synchronized and plays the same music at the same time, effectively boosting the speaker volume for each device you add.
Seedio works surprisingly well. Running it on an iPhone and an iPad created a noticeable volume improvement. Seedio is free for a limited time in the iTunes App Store.