@Dave Moore Thanks for posting in our Q&A.
Based on my research, I find that if we want to use iOS device user enrollment, there is some prerequisites that need to be met in the following article.
https://learn.microsoft.com/en-us/mem/intune/enrollment/ios-user-enrollment#prerequisites
When we select Secure entire device, it is device enrollment. However, when we select Secure work-related apps and data only, it is user enrollment. If you want to enroll personal iPhone to intune, we suggest to use device enrollment method.
Thanks for understanding and have a nice day.
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