Not sure what bit rate TV is at, but one 4K YouTube stream can take up to 68Mbps, and 8K even more.
We're on 400Mbps, and even then I manage to block internet for others when I download a large file at full speed.
That's more of a router/QoS issue. A large download shouldn't negatively affect quality for other uses, especially VoIP. If the place you're downloading from has a pipe bigger than yours and can saturate your bandwidth you're going to need to implement some kind of rate-limiting/queue management.
It, at the very least, hides more than it illuminates in that 68Mbps is an order of magnitude higher than an average 4K video's bitrate over it's duration