The Slysoft team has fantastic products. Use AnyDVD for decoding (happens automatically in the background as soon as you insert a DVD) and then CloneDVD to convert to the mobile format and resolution of your choice (they have a native iPod setting so an iPhone setup can't be far behind). Even without a native iPhone setting you can specify the resolution and file type so the coverted files can be easily played on the iPhone.
I've been using these for a couple years both for just DVD archiving and to put my daughter's cartoons on her video iPod.
Support is fantastic and they release updates very frequently.