Toddler eating problems

My almost 3 year old does not eat😭 I don’t know what to do anymore, I insist all day everyday for him to eat and he will not eat. He will have a couple bites for breakfast and not eat the rest of the day. If I don’t insist or make him anything he will not say he’s hungry or eat all day. I feel so bad bc he’s not getting anything in his system or nutrients that he needs. I feel that everyday it gets worse and worse, I have told his pediatrician about it and says it’s just a phase, but I don’t think it is anymore. I try to make him different things or ask him what he wants to eat that day and he won’t eat. Or you know kids like eating out like happy meals or pizza and stuff so I even try to give him that so he can eat something but he won’t even eat that😭

Should I be concerned or is it really just a phase?

Any suggestions that I can do to get him to eat?