haven't tried it on the mobile site but have done OLCI and seat selection on my iPhone. The key to scrolling through the cabin is to hold your finger down as if the magnifying glass would come up then scroll further up or down (depending on where you want to sit) without taking your finger off the screen.

The biggest problem I have is that OLCI on the full site crashes my safari at least three or four times before I complete the process. Tests the patience of a saint...

Will definitely try the mobile site next time I fly.