Bigger answer button for older persons?

I watched my 80-year old mother in law failing to answer a callback from her health provider.

I think it would help if the answer button wasn’t the tiny minimum size set by the guidelines. Most of the screen would be like it. I also think the answer button should be twice the size of the decline button.

Is it possible to just increase the sizes of these buttons? She does not have any need for other accessibility features.

If it would apply to Facetime calls as well, it would be fantastic.