Look here.
Specifically for your issue, the summary is that in download direction, it only makes sense to throttle traffic whose source can detect that it is throttled and can adjust to that (which is all TCP traffic and a few advanced applications using UDP as transport), but throttling download traffic whose source doesn’t get any feedback about that has no effect. The throttling of download is actually made by queueing the packets in WAN->LAN direction.
So depending on what is the actual traffic which interferes with your videoconferencing sessions, you may or may not be able to make more space for the videoconferences in the download direction of the uplink or not.