Let's complete phone-* sounds
In the Sound Naming Specification phone-failure and phone-hangup are present, but not provided by xdg-sound-theme. Just add RO' ' SIT as phone-failure and something similar to IOS phone disconnect tone as phone-hangup.
Completing xdg-sound-theme is important because programs use sounds from Sound Naming Specification only if provided by xdg-sound-theme. So let's complete at least some of his groups, starting from phone-*.