Video saved back to phone the imagen is too small

A video that I had in my phone I downloaded to my computer , trim the video , saved to mobil and them saved back to my cellular, now when I watch the video in my cellular vertically shows the imagen top to bottom is ok but them left to right  is really narrow impossible to see it and if I turn the cellular horizontal  is too small ,don't know how to fix this problem, Thanks, Armando