RipIt is a great little Mac application which enables you to rip DVDs. It has been designed for both Mac OS X Tiger and Leopard. The basic concept is to rip the audio CDG files on your computer into a "raw" file, so that it can be burned onto a blank DVD. There are a number of other advantages to doing this as well, such as making backups of your data or storing it indefinitely on external media. I will go through a short demo of how to rip a disc with RipIt below.
Ripping a DVD with RipIt is essentially the same process as ripping a music CD or movie DVD - you just have to rip the video out of the original DVD. On installation, you are simply required to insert a blank DVD into your Mac, and then insert one of the blank DVDs that came with RipIt. RipIt automatically identifies the best video codec for your Mac (ffmpeg) and lets you know which one to use for the job. Once that's complete, it will begin to rip the video on your Mac.
As far as the differences between a Mac and iPhone are concerned, I guess that iPhone's lack of a DVD burner would make that particular task rather harder. Regardless of that, the iPhone can also rip videos and audio CDs, and has a better camera than the Macs even when it comes to pictures. This is why the iPhone is considered to be better than the iPod when it comes to multimedia usage. Ripping a video or music CD or movie out of your iPhone using an iPhone is like putting together a CD inside a CD and putting it in your pocket. For that reason, I suggest using the iPod to do this task, especially if you are going to be travelling, since there's no chance that the CD will rip properly on a plane.