If you blocked someone directly from a text conversation:
Finding blocked numbers on your iPhone depends slightly on which version of iOS you’re running, but the core process is simple.
To search or view your blocked numbers on an iPhone, you typically navigate through the app to find a consolidated list . While iOS doesn't feature a dedicated "search bar" within this list for specific numbers, you can manually scroll through or use the main Settings search to jump to the right menu. How to View the Blocked Numbers List
If you want to block a new number: