how to test if select option is seleted

I’ve tried the following statement:
<option value="[+id+]" [+phx: if=`[+id+]`:is=`[*id*]`:then=`selected="selected"`+]>[+pagetitle+]</option>
but it doesn’t work.
This line is in a chunk, and the chunk is parsed by Ditto.
What I’m doing wrong?

Thanks.