Boy potty training..

Sativa

Hi, I need some help. I have recently taken custody of a little boy who turned 3 in October. He still wears a diaper. He is deathly afraid of the toilet and cries when put on it. We tried stand using cheerios, just using a pull up, using just underwear, he cries and screams if he naked he has an issue with no clothes he wont even leave his shirt off. We also tried a sticker chart and candy/prize box. I am not sure how to approach this. I havent potty trained a boy before. Im out of ideas.