I thought that was just the inability to form images in your mind, I've never meet someone with aphantasia but I thought they could still imagine things, they just had a hard/impossible time formulating 3D realistic images. That's not really related to whether you have a "dialog" or not.

Also aphantasia isn't considered a disability in the medical sense.

I think aphantasia is just the inability to form pictures in your head, isn't it? That doesn't necessarily mean they can't imagine things, just that they don't attach a visual component to the process