I got the idea for this tutorial from "fireraining". Ripping DVDs and putting them onto the iPhone is very easy to do. You will need two programs: DVD Decrypter 188.8.131.52, and Videora iPhone Converter 2.25.
Install the DVD Decrypter.
Start the DVD Decrypter and insert your DVD. Go to the "Mode" tab and select "IFO I".
Go to the "Tools" tab and select "Settings...".
Go to the "Stream Processing" tab and check the box for "Enable Stream Processing". Deselect all the check boxes except for the first video and first audio streams listed. Click the graphic/button with the DVD and the hard drive on it to decrypt your DVD.
You'll get a status screen so you can keep track of the ripping process.
You'll get a pop up and a tune to let you know the ripping succeeded. Close the DVD Decrypter.
Start the Videora iPhone Converter. Go to the "Convert" tab.
A pop up window will appear, navigate to where you stored your DVD rip at, click it and click the "Open" button.
The converting will start immediately. The time remaining bar is at the top of the current window.
When it finishes it will prompt you for where you would like to save the file and then it will load it into iTunes for you.
Connect your iPhone. Go to the "Video" tab and in the "Movies" section, click the "Sync movies:" box and click the name of the movie you want to sync. Click "Apply".
iTunes will give you status as it copies.
When the sync is complete, click the disconnect button.
On the iPhone click the iPod button and go to videos and enjoy your movie. Click the double arrow on the screen in the top right corner if the movie looks zoomed in too much. Sometimes the iPhone does this to fill the screen.