Audiobook from CD to Iphone

I have an audiobook that I could only find on CD. I would like to have it on my iPhone and have it know where I left off when last listening.

It used to be you made it in AIFF files and ran a script called "make bookmarkable" - but so many things have changes in iTunes.

I have it now as MP3 files, but they aren't staying in order on my phone. Any suggestions?