GrapheneOS and Android are both based on AOSP, and calling/texting is such basic functionality for a mobile OS that I doubt that GrapheneOS’ implementation is much different from Android’s, if at all.
I’ve been on GrapheneOS for the past year or so, I’ve never actually enjoyed using my phone as much as I do now. No Samsung apps I can’t uninstall, no Google spyware, the only stuff running on my device is stuff I want it to run, the way I want it to run.