Do I have to write GRE to apply to physics PhD programs in the US?
Every university in the US has its own policies. There is no national educational system in the US. 

If you want to apply to a place for which it is mandatory then it is mandatory. Otherwise not. However, for those places for which it is optional it might be a way to bolster your application, so consider that, at least. 

Every graduate school is looking at your application materials for evidence of success. If you can show that and also meet the rules then you have a chance to be admitted. But the rules aren't normally optional.