windows movie maker edited movies appear small on the Iphone6 screen

Hi, please help, I edit my movies using (windows movie maker) then save them to HD (High defeniton display) setting, the movie's display size is big on the PC, but when I transfer the same movie to Iphone6, the screen size of the video shrinks, it looks small, it does Not fit the screen, I tried sending the movie (without Editing) to iphone6 and it fit the screen perfectly, but after editing using movie maker, it just shrinks on the screen of the Iphone, why ??? I tried all the (save movie) settings on movie maker, still the same result, please help :(