Copying over movies

I know this is a silly question, but I'm coming from an Android device to the iPhone 6S Plus and trying to figure out an easy way to copy movies to my iPhone. It was pretty straight forward with my Android device - I just chose which movie I wanted and copied it directly to the Movie folder. I tried it on the iPhone and it requires me to first copy movies to my Macbook and then sync it to the iPhone. Okay, great. I have some of my movies added to my iPhone. So I deleted the movies from my iTunes library to conserve space on my Macbook. How do I add additional movies to my iPhone without erasing the ones that are already stored on my iPhone now but removed the originals from my Macbook?