There should be something that appears in the kill feed when a phoenix ult is killed. Usually, the only way to know is by looking at the ults or a teammate comms, which aren't very reliable. It would just be a nice quality of life change.

It's kinda annoying how after you kill the bot with Jett's knives, you have to get another set out. Hard to practice her knives that way. Hopefully Riot adds this someday so we can practice without trouble.