Hello David,
What tool are you using to create your PROFINET configuration? I know there was a bug in the Phoenix PROFINET Configurator which prevented the usage of e.g. Siemens I-Devices. This shall be fixed in later versions of the tool. (Version 1.31.38 shall work). I use a Siemens S7-1500 as an I-Device in my setup, and it works fine, so it should be possible to configure without problems!
Best regards,
Emil