How do you kill Adamus Phillida in Oblivion

One way to do it, and probably the quickest, is to open your console, (Press ~)
Click on him, (Make sure when you click on him his ID is shown at the top of the screen) and first type the following without quotation marks:
''SetEssential 0''
^Note: The space between SetEssential and 0 is required.
Then type ''kill'', (No quotation marks) press ~ again, and he should drop dead.
If you prefer to fight him to the death, instead of typing ''kill'', just close console after typing ''SetEssential 0''.
This method can be used for any NPC who normally just goes unconscious.