What you need to do is implement QoS. QoS is a very large and complex subject (too broad for details here, as entire books are written on how to use it) that encompasses everything from classifying and marking packets, to performing some sort of action (shaping, policing, queuing, etc.) based on the classification/marking. To properly implement QoS, you need to have a comprehensive set of QoS policies that are implemented consistently across your network.
Also, understand that your QoS policies and markings will not work on the public Internet. You may be able to pay your ISP to respect some of your QoS policies and markings, but QoS on any traffic sent from your ISP to others on it way to the destination will be ignored. You also have no direct control of any traffic coming from the public Internet until you have received it on your network, where you can properly mark and treat it.
To properly treat the traffic, you need to first mark it, and you want to do that as close to the source as possible, ideally on the source device, but you can get into trouble simply trusting applications. Practically, this means marking on the access switches as the traffic comes into the access switches.
Some Cisco switches default to marking everything coming as
BE (Best Effort). You probably want most traffic to be marked
BE, but you will want VoIP data to be marked
EF (Expedited Forwarding). You will also want to mark some things, e.g. control traffic (VoIP control, routing protocols, etc.), with a higher priority, but not
EF, and you will want to mark some things, e.g. server backup, with a lower priority.
Once you have your traffic properly marked, then you want to use that. Cisco switches can do some limited queuing, but you certainly want to use the markings on your routers where you can do queuing, policing, and shaping. Typically, you will want to set up a priority queue for VoIP to guarantee some bandwidth, and you really want to police any traffic beyond the priority queue bandwidth. Other traffic will have various queue sizes.
You really want to keep it fairly simple. A rookie mistake is to try to set up markings and queue for every different traffic type. The simplest, and often best, QoS policies leave most traffic as
BE, and you only mark and treat differently any exceptional traffic like VoIP, control, or bulk traffic.