I assume you went through the options of the phone and the TV and turned whatever off to try to stop it, or force manual confirmation, or maybe remove it from your TV's list of devices it likes. I have seen bugs cause similar things in the past, though I would still suspect some kind of "helpful" program or option getting in the way. On the other hand most "smart" TVs are anything but so I can well believe one is so poorly coded as to cause things like this.

Simpler option.

If your home network is more "things go on the internet" and the things on it don't need to speak to each other (no shared printers, file stores, in network streams, LAN games...) then a lot of modern routers will allow you to block devices from speaking to each other on it. Possible option 2 related to that is if you have a guest network then that can be an option, and it might be isolated by default. Shuffle the TV or your phone onto the other and that is that.
You could also set up a secondary router and so something similar but unless you are also going to use it as a signal booster than maybe don't go there.

Less brute force is you could possibly isolate your phone or the TV and just that. Options to do this in the router vary with what your have (some may play with a DMZ, vlans or maybe a simpler option), though your basic home router might not do it in software. Forcing one to operate on a different subnet on the other hand would isolate it, simple way to do that is to set a manual static IP address on another subnet. That way if you do want to broadcast to the TV you can flick it back to DHCP and then use as normal before going back to static.

Again far better to find whatever option is causing you grief but some fairly basic network configurations should be able to get done what you want to get done. If you don't need the functionality now or "just quickly" in the future then my concerns become far less.