Is there any data that apple can access on my phone that I cannot myself access? If so, what would that be and why?

I am wondering if I have the right to ALL potential data coming off my phone or if there is, say, diagnostics info that I cannot access Myself but apple can in order to run diagnostics. And is the logic if yes that this info is subject to IP because it shows the code of the software or the build of the hardware or something like that?