I just checked this in Simlab (Windows) on my system, and the only option for .ZIM file export says ipad. The .ZIM file is cross platform, so they probably should fix the export dialog box and get rid of "ipad" because it is confusing.
You should be able to IMPORT the .ZIM back into Simlab to test it. If this works, it could be the file is corrupted somehow on your phone. It could also be the file is just too large to be opened using the memory and processor on the phone.
How many polys are in the file, and how big are the textures (if any)?