what about Graphene?

GrapheneOS only supports devices with isolated radios including but not limited to cellular. It's one of the hardware requirements:

https://grapheneos.org/faq#future-devices

The radios on the supported devices can't access the microphone, GNSS, etc.

GrapheneOS has never supported a device without an isolated cellular radio since that isolation was in place even with the initial Nexus 5 and Galaxy S4. However, some of the devices prior to Pixels did have Broadcom Wi-Fi/Bluetooth without proper isolation similar to laptops/desktops. Nexus 5X was the initial device with proper isolation for Wi-Fi/Bluetooth due to having SoC provided Wi-Fi from Qualcomm. Pixels have avoided this issue for integrating Broadcom Wi-Fi/Bluetooth. Nexus devices left this up to companies like LG, Huawei, etc. and anything not done for them by Qualcomm tended to have security neglected. Qualcomm has taken security a lot more seriously than other SoC vendors and typical Android OEMs for a long time and provides good isolation for most of the SoC components.

Don't believe everything you read about smartphone security and especially cellular radios. There are many products with far less secure cellular radios which are far less isolated but rather connected via extremely high attack surface approaches including USB which are claiming those are better. A lot of the misconceptions about cellular come from how companies market supposedly more secure products which are in reality far worse than an iPhone.