Block everything except VoIP on a gateway?

Hey!

We have multiple gateways to handle our heavy Internet requirements including VoIP and Skype for business. The issue here is that due to the usage, Skype and VoIP call quality is being affected severely. Now we have added an additional High speed Internet connection and a gateway only for the multiple VoIP and all the Skype requirements. We want to block all other Internet traffic except those of VoIP traffic in this gateway. Is it a feasible solution or even a possible one? Is there a better solution? I hope someone could provide a helpful solution.

Thanks!