I think you’re conflating two very different cognitive processes. Aphantasia is very specifically the inability to visualise Images. Maybe, in a broader sense the inability to visualize (specific) senses in general. Lack of an inner-self and the resulting inability to self-reflect might be a thing but it sure is a very different phenomenon from aphantasia. Your inner self isn’t a physical sensation that you’re trying to visualise a memory of. And even anendophasia, the lack of an inner monologue, which is closer to what you’re describing than aphantasia, although still not quite it, does not seem influence self-reflection capabilities.