The green flash is real, it can be explained by ordinary laws of physics and, best of all, is eminently photographable. I live in an ideal location for observing it, as for most of the year the sun sets over the Atlantic. Raggytash will confirm that. We were having a pint at the Bay View Inn, conditions were ideal and he was poised ready with his camera. Unfortunately, it's possible to be so preoccupied with the zoom and the little screen to get your composition right that you can forget to look at the sun at the crucial moment. Think how hard it is to catch a flash of lightning with a single shot when you're waiting for it, finger poised on the button. I reckon you'd see the green flash from here maybe ten times a year if you were really vigilant. Unscientifically, I've worked out that your chances are best if:
the sky is completely free of mist or dust haze
there is no cloud at all near the setting sun
the sea surface is smooth, unruffled by too much wind

I reckon your best bet is to shoot the sun with a good video camera with proper optical zoom, not an iPhone. It's worth trying the burst setting on a stills camera, though on the modest cameras I use this yields lower quality shots than taking single shorts on the best quality setting.

When conditions are ideal you'll always get a little clutch of people on the beach at Widemouth Bay trying to get that shot. I think you'd be better off raised a good few metres above sea level, or standing on a clifftop. Or in my back garden, 100 feet above sea level. :-).