I had the opposite problem on my Phantom.
The pedal was quite difficult to get to disengage, so the pedal stuck up all the
time and I couldn't get it to drop down into the other (disengaged) position.
What I found was that you need to pull the pedal up and then slide it back a little to get
it to lock in the "actuate" position.
Conversely you need to slide it forward a bit to get the pedal to disengage, then it will fold down flat.
Somehow the design of the release mechanism seems to have made the pedals very hard to slide (in my case and perhaps yoiurs as well) and you need to play with it a bit to
A/ Figure out just how to slide it so it moves for the engage/disengage positions.
B/ Operate it several times so the "stickiness" works loose and you can fairly easily slide it between the two positions.
It will work, I'm pretty sure, it's just the motions you need to get the thing to slide are very non-intuitive and need to be figured out.
Hope this helps,