That has been the position taken by Apple and others. I disagree. It is possible to "program" the phone to answer calls by voice commands.
In order to accomplish this a person first has to identify the areas on the screen that are utilized to answer calls by mechanical means. You can do this with any marker that is visible and that can be erased. You will need to do it twice.
First call your phone and circle the areas that you will either "slide" your finger across or "tap" to answer the call. These will be two separate locations and will require two separate phone calls to find and mark locations (call without having anything opened on your phone and then call again while you have an app open).
Disconnect and proceed to settings.
Scroll down to Accessibility and select.
Then scroll down to Voice Control and select.
Make sure that "voice control" is off and then scroll down to "Customize Commands" and select.
Scroll down to "Custom" and select.
Scroll down to "Create New Command" and select.
You will have to type a new command for each area on the screen that requires mechanical action. I typed "Answer" for one position and "Answer phone" for the second. You obviously cannot do both at the same time.
After you have typed the command you have to select "Action" and then select "Run Custom Action".
You will then have the opportunity to select either of the two locations on your screen you have marked and either "tap" or "slide" your finger as required.
Save that action and then repeat the process for the next new command and the other location on your screen.
Then go back and turn on "Voice Control".
Your phone should answer an incoming call by duplicating the "Custom Action" that you have programmed for which ever "answer bar" appears on your screen.
I got the idea for this by watching a guy on the internet set his phone up for Siri to unlock via voice command.
I have done this on two phones successfully.
My first command is "answer" and if that doesn't work I immediately say "answer phone" (I can't always remember which command is for which bar).
I don't know if this will work on all iPhones.
I had to attempt this because the person who owns the other phone is going blind. I hope this helps others.