The Signal messenger and protocol.

I've recently started using signal and getting some of my contacts switched. I have a signal contact that's in my iPhone contact list, but isn't linked and I can't find any way to get that link created. He's tried toggling the privacy->phone number options on and off, the "who can see" and "who can find me", with no luck.

One possible clue - my first signal connection to this contact was in a group chat, I texted the link and he joined signal that way. No idea if relevant.

Any thoughts?