Toddler only eats a few foods

He's so picky at the moment. He never used to be so I'm hoping it's just a phase. But trying to get him to eat anything is so difficult. He only eats certain food, but he'll eat a lot of it. For example for tea I made a roast chicken, with roast potatoes and veg. He only wanted the potatoes but he ate loads of them. After tea I normally give him Greek yogurt with some berries, so I offered that and he ate the lot. I tried offering his chicken and veg again but he wasn't interested and asked for a banana. I give him a vitamin but I'm just worried that he isn't eating enough variety anymore. He seems to only want fruit and bread/potatoes things.