I'd also say that Full Throttle is the easiest, however if a smartphone can't handle it then I'd recommend Monkey Island 1
I'd strongly disagree that Full Throttle is the easiest... It may be the shortest
, but unfortunately it suffers from a LOT of annoying puzzles that aren't necessarily logical (as I discovered when I recently replayed it).
LOOM was commonly known at the time of its release as being an "easy" adventure. (Sierra even lampooned its easiness in one of their games.) Monkey Island 1 is certainly a friendly place to start, but it's not the easiest.
Loom is the way to go.