Since at last count, biologists had documented more than 6,000 physiological differences between male and female humans, I don't buy the argument that what defines male or female, and what distinguishes one from the other, is simply the presence and partial function of the external genitalia. Nor do I buy your argument that a surgical creation that somewhat resembles a penis in visual appearance and with mechanical assistance might be able to mimic the some of the behaviors of a penis is actuall a penis. And I certainly don't buy the preposterous claim that because sometimes a faux phallus made out of female arm skin have been or can be connected to some nerves in a female pelvis this means a female with a surgically-created faux phallus "can feel things like how a non-trans man feels things through his penis."

But if for the sake of argument I were for a moment to accept your premise that one and only one male organ is reflective and determinative of a man' sex, then I'd argue that you're focusing on the wrong organ. Because as it so happens, the testes are way more important than the penis in male sexual reproduction - and reproduction is the whole reason why sex exists in the first place.

After all, it's the testes that produce the male gametes; the penis is only a delivery vehicle for the male gametes.

What's more, the testes are the organ that produce the bulk of male sex hormone testosterone that causes male bodies to develop in such distinctly male ways. In other words, the testes play the central role in male sex in two crucial ways; by comparison, the penis is ancillary.

In the modern era of medically-assisted reproduction, it's possible for males to father children with sperm extracted directly from their testes. Men with total erectile dysfunction, micro-penises too small to inseminate through penetrative PIV sex, certain DSDs, and penis damage or amputations due to disease or injuries have done exactly that. Even males with DSDs that often cause the most serious malformations of the external genitals, including the apparent absence of a penis at birth and undescended or wholly internal testicles, such as 5-ARD - the male-only DSD that Caster Semenya has - can produce viable sperm from their testes.