Without knowing the detailed specs of your video (or the detailed specs of your computer hardware), I'd say that most likely it's that your phone video using a high compression that Premiere Elements has to decode and then re-encode. And that can take time.
With standard video on a decently powered computer, it usually takes about the running time of the video to create a DVD. But phone and other non-camcorder video can take twice the video's running time -- or more, depending on how fast your processor is.