Premiere Elements 10 is a pretty ancient version of the program. There was no real support for other than traditional camcorder video at that time.
Premiere Elements 15 will definitely edit iPhone video.
but how can it have no problems with canon 60d video, also the same file format? is there a difference in iPhone video and 60d video?
I also tried to duplicate the file, to rename and change the file type to mp4, this did not help premiere elements.
You might try a "work around"!
If the Canon video works, establish what the specifications are. Then, run A COPY of the iPhone video through the free utility called Handbrake and convert it to match the Canon video.
Good luck with your project!