Hopefully you have found a solution by now?
If so please see this response as guidance for others who may land here with a similar need.
I wished to block a nuisance caller recently and have found that most solutions to blacklisting are less than helpful and are not simple, free, nor striaghtforward to enable.
(I live in the UK where true blacklisting, (where that means a specific calling number block, is only available at the network level in the thelecommunications system, telephone service providers are reluctant to offer users simple control of who calls you. (It is very easy for a nusance caller to simply use a different number each time they wish to call you). Blocking a specific calling number may not be effective against those who persist with calls and use banks of different calling numbers.
In the UK there are a number of paid for services from telephone service providers such as "BT inclusion", and Virgin Media "anonymous caller rejection", that have the ability prevent reception of unwanted calls.
From third parties for example www.ambushcall.co.uk a service (at a cost) gives some user control. Control for withheld number callers (iPhone "Blocked" calls) requires manual intervention if you receive a call from a blocked (number withheld) caller declining the call can divert the caller to a message that informs the caller that the number called is no longer in use. If you receive calls from legitimate blocked numbers, e.g. hospitals or doctors, you may not want the complication of divertion and calling back the legitimate caller.
Ambushcall service has the merit that they do not need your contact list to produce a "white list" of sorts as many iPhone Apps do require from you. You may consider that giving your contact list to a thrid party unacceptable.
None-of the third party services I have found offers a network level blocking service.
Introducing such a facitlity in harware to a moblie phone that would operate globally with all telephone service providers and remain leagal for use in all countries, while not introducing (further) potential security breaches to you personal data, may be unatainable for now?
Good luck with your searches.
Thank you for your helpful and informative response.
I do not now see the part of the OP's question that asked for a link to the Apple feedback page.
Perhaps taht part OPs question has been edited out since the original post.