Why are the default Skyboxes really low quality on mobile (iOS)?

I used one of the default skyboxes, however this happens with all of them. It looks fine, but after I build the game for iOS, the skybox suddenly becomes really bad quality. The mobile skybox doesn’t do anything either. I tried making a new project, and the same thing happened. So at this point I can only assume that its the skybox’s fault, what do I have to change to get it to work well on iOS, or do I just need a new skybox altogether? Here is a screenshot of what it looks like in the editor:
alt text

Thanks, any help is appreciated!

you must choose on the picture option the format from compressed to truecolor

Try changing the import settings of the picture files.