I use a Bose Soundlink III with my iPads without any problem; in fact, the sound can fill a large room. Are you sure that the phone and the speaker are properly paired? The issue may be that the Soundlink has its own volume controls which may be set too low. Have you tried to increase the volume on the speaker as well as on the phone? Have you tried using another device with the speaker? Have you tried using a cable from the earphone jack of the phone to the aux input of the speaker? If the speaker works with another bluetooth device, it may be a problem with your phone (or that your phone and speaker are not paired). If the speaker doesn't work with other devices, then it may be a problem with the speaker.

Good luck.