On iOS devices, it’s a bit difficult when it comes to reporting or blocking unwanted calls or messages. In fact there is no official way of doing so, unless that message is being sent via iMessage, but beyond that there isn’t much you can do. However as noted by 9to5Mac, that could change with iOS 12.
It appears that one of the changes that Apple is making to iOS 12 is to allow support for third-party apps to create extensions that can handle the blocking and reporting of spam calls and messages. This means that users can expect to see options available to them that would allow them to report a call or message that they think is spam and that they don’t want to see again.
However the only downside to this is that the onus of implementing this feature is largely dependent on developers and whether or not they want to take advantage of it. This is not a native built-in feature implemented by Apple, so if developers don’t choose to implement it in their apps, then we guess nothing would have changed.
According to MediaNama, they speculate that this change could be Apple’s concession to the TRAI telecommunications regulator in India, where Apple had previously rejected a government designed app that would block and report unwanted sales call. Apple had cited privacy issues as the app wanted full access to your calls and SMS logs, but perhaps this feature could be a middle ground.