The op is asking whether or not you can continue using the phone with a active incoming call with iOS 13. You can’t.If you mean a caller id's photo showing the entire screen, you can fix that and use the smaller circle version by using a 512x512 or less resolution for your contact pic. I also hate the full screen caller id as well.
Pretty sure that a change related to something like that would have been at the very least touched upon in some way during the keynote and/or the preview web site.please let us know