[General] Dlink 880L QOS and Choppy VOIP During Streaming

Hi I am curious if anyone has any tips for using QOS on a Dlink 880L, in order to prioritize VOIP. I have a 25down/10up Mbps DSL line, and have tried the QOS on the router. I still find VOIP to be choppy when my wife streams on an android box. I use a SmartRG 505n modem in bridge mode, with the Dlink 880l handling the PPOE, and a SPA 2102 (behind the router) for the VOIP. Does anyone have any suggestions on how to ensure VOIP stays clear when the internet connection is otherwise highly used? Does the Dlink QOS work at all? Is port forwarding important, if VOIP is fine when the line is unused? Thanks in advance.