Having the same issue and this is a dealbreaker for me.
Researching and it seems that basic phone functionality (SMS/calls, including notifications) is problematic with secondary profiles. I've tried every SMS app under the sun and they don't get through to the secondary profile, images are missing from MMS, notifications don't clear properly, outbound messages appear twice, etc. Very frustrating.
It's not a carrier issue.
The whole point of GrapheneOS for me is to have a least-privileged user - e.g. owner is root and secondary profile is my daily driver. If I have to use the owner profile for basic phone functionality, then that defeats the purpose.
Unsure if this is a GrapheneOS issue or from upstream AOSP, but if I need to use the owner account to do basic phone stuff, then I might as well go back to stock Android . . .