How do you raise the volume of a speakerphone on an S5?

[AC Question]

My colleague's S5 has oddly low volume for her speakerphone.

It is Verizon. All volume settings are at maximum level. Music, notifications, everything else sounds right, but if you turn the speakerphone on during a call, the volume is noticeably lower, to the point of being unusable. Please help! Thanks