Will an examiner be able to tell the difference between pictures taken by the iPhone X or a DSLR camera?

I'm doing GCSE photography and I have a really high quality moblie camera. However, I was instructed to use a DLSR camera. (Keep in mind when taking photos I will take them in the optimum conditions for iPhone cameras.) Do you think I could fake it?

Yes. The file's metadata will say what type of camera you used.

Printers, and Digital Cameras place an encoded stream in their photos, which identify the specific, ID, Camera, Printer, time and date.

If using a DSLR is the only requirement it's very unlikely anyone will be able to tell the difference - assuming the EXIF data have been removed. But why is it mandatory to use a DSLR in the first place? Are you expected to use any specific settings, focal lengths or whatever? I'm guessing you'll be asked to provide the specifics for your pictures - unless you understand the differences between sensor size and how the crop factors will influence things, you'll be caught out!

Drop out of your class, you're wasting space that someone else would appreciate.

Why take the course if you won't use the required gear? If you can't afford the DSLR yet, then take the course when you get one.

Why the hell are you even taking this course? What do you think you are going to do when the assignment requires shooting a scene with a shallow depth of field and a long shutter speed with second curtain sync? Your damn phone is like bringing a knife to a gunfight. Either get the right equipment or get out of the course and stop wasting your time and the instructor's time.

Have you asked the examiner if alternate equipment is acceptable. The DSLR could be just left over from when all phone and other digital cameras were really poor quality compared to what you could get on a DSLR. So maybe a phone is OK.

EXIF data tells all about the photo and the equipment used. If you are required to keep this data then you'd have to find a way to spoof the data (probably wouldn't be that hard, but never thought of doing it) to make it show a different camera and such.

At the end of the day, any photographer will tell you that it is the photographer and not the camera that makes a good photo.

Probably, especially if the data is included.

With metadata intact it will show everything, including the gear, setting, and software used.
If no metadata, if the examiner good enough, the person will know for sure.