On Thu, 12 Jun 2008, Hans Hagen wrote:

> Maurí­cio wrote:
>
>> used ‘ϕ’ in a math formula for one of his papers and Context
>
> it showing up depends on what you use (mkii or mkiv), if the character
> is defined, if the font has it (in text mode) etc etc

For mkii you simply need to add \enableregime[utf8] in the beginning. It 
should work out of the box in mkiv (assuming you are using the default 
latin modern fonts).

Aditya