No. It is not ‘transphobic’ not to want to date a transgender person.
Homosexuality is when a person experiences physical attraction exclusively towards other persons of the same sex. Heterosexuality is when a person experiences physical attraction exclusively towards persons of the opposite sex.
A transgender person has not changed sex. It is not possible to change sex. The surgeries that transgender individuals may have do not change their sex – they only approximate the appearance of the opposite sex.
Since a transgender person has not changed sex, a female who asserts that she is a man will not be attractive to homosexual males, and a male who asserts that he is a woman will not be attractive to homosexual females.
Sexuality cannot be changed. A homosexual male cannot ‘learn’ to be attracted to females, and a homosexual female cannot ‘learn’ to be attracted to males. To state that they can do so is generally regarded as anti-homosexual.
If a female looks like a man, wouldn’t gay men be attracted to her? If a male looks like a woman, wouldn’t lesbians be attracted to him?
Humans are adept at identifying the sex of other humans around them. Your sex is identifiable not just by your external reproductive organs – it is visible in the shape of your hands, your musculature, the shape of your body, the shape of your face – it’s even visible in your gait, gestures, and facial and vocal expressions. Humans can generally still reliably identify the sex of a person even if they have changed many aspects of their appearance to mimic those attributed to the opposite sex.