Is there any way to remove AppleTV from the speaker list on the Phone app in iOS? I am running iOS 13.1. I tried disabling Allow calls on other devices but that did not solve the issue.
Turn off air play on the apple tv.
Otherwise the only way is to place the apple tv or iphone on different networks. This can be done by creating a vlan and a new essid that tags network traffic to that vlan. Plus routing rules to give the vlan network access to things it needs (internet).
Or possibly create a new subnet and setup routing so the 2 subnets cannot communicate but still allows Internet access.