I think I understand what you mean a bit more now. So just to be clear, is the inclusion of the feature phone purely to prevent you from using a device capable of accessing social media? If so, it makes sense. I just wanted you to understand that I don’t see much of a privacy benefit in it.
But if you were looking to divide things up for privacy reasons, I’d suggest considering my recommendation for the GrapheneOS setup I alluded to earlier which involves using VoIP numbers. Michael Bazzell has a “Mobile Devices PDF” book that goes into detail on this subject if you’re interested. He’s not selling it anymore as he wasn’t making enough money due to piracy but still posts updates to his blog. I won’t condone anything illegal but I’ll just mention that since he is not selling it anymore, it can no longer be legally obtained and people pirating that book today aren’t hurting his business as there’s literally no way to pay for it anymore. Anyone looking to support him today can pay for his UNREDACTED magazine which will be continually updated.