TBH it really depends on your threat model. Yes grapheneos is great for privacy minded and secure smart phone options. However, just by having a sim card in your phone and connected to cell towers on your network and not in a faraday bag you are not at all private to state-backed entites. If you use sms at all your messages are not private. If you receive push notifications on your smart phone the metadata, and in many cases the content itself, is retrievable and not private.

I can’t recommend graphene for privacy, however if security is your main concern it will definitely do that well.