I am playing a Robo Substitute from my hand to my Bench, but my opponent used Venomoth's "Dizzying Wind" attack last turn. Do I have to flip to play it?
Yes, Robo Substitute is a Trainer card when it is played.
Source: Phantom Forces FAQ (2014-11-13), TPCi Rules Team (2014-11-13)

Relevant cards

Note: All applicable cards may not be listed below.
XY4_102
XY4_2