1) If they're commercial movies, they're copy-protected (and you don't open them - you own the plastic the DVD is made of and you own the right to play that DVD). So the first ting you have to do is defeat the copy protection (which is a violation of the DCMA).
2) Once you've gotten the audio and video off the DVD, you have to convert the files into a format that you have an app to play. There are many different formats and many different conversion programs. Then you package those files into a "movie" and put it on the phone.
There are websites devoted to DVD copying that can help you better than we can.