Well since you wont be performing any procedures, I can't see this being in conflict with Australian law. This could be a good opportunity to impart good advice, explain to him that he is still growing, and that there is much more to life, health, and happiness than sheer size.
I wouldn't be surprised that the proliferation and ease-of-access to adult content on the internet is exacerbating male penis-dysmorphia (I feel like I'm the only one hammering on about it), and you can also point out the importance of consuming any content in moderation (without necessarily accusing him of being a "pervert" lol).
I'd argue that legitimate
Phalloplasty practitioners would yield better consultation and advice to a 14yo than any family doctor, that's just my 2cents. If I were in your shoes, I'd probably have a sincere talk with him, or at the very least, give his parent(s) a stern message about not affirming their son's dysmorphia by taking him to a doctor for size enhancement.
Now if he has micro-penis or a heavily buried penis, this would justify medical consideration if possible, in my opinion.
I wonder if this kind of case is a rare occurrence or will continue to grow as social media, pornography, over-sexualized pop culture, and increasingly unrealistic beauty expectations become the norm. I'm all for self-improvement, and that includes elective medicine, but 14 is too young to be taken into a cosmetic procedure.