As a PhD student, should I list a conference travel grant in CV?
I would suggest listing the participation, but not the grant. At the point you are, starting the doctoral studies, it will have little to no effect in any case and by the time the CV becomes more important you should have more substantial things to list. 

Alternatively, if you list the participation and simply note (funded) after the reference, it would be fine, I think. But don't try to make it sound like more than it is.