The full phone number includes the country code, which is 1 for North America. The + is needed now, because a lot of countries use 1 as the first digit of an internal (to the country) number.
In the US and Canada, a call with or without the one goes to the US or Canada, so it doesn't matter if it's there or not. (It messes with some call blockers, but if the call blocker is done correctly [by the developer] it ignores the + and the 1 if they're there, but blocks the following phone number. A 0-9 match or a 2-11 match should be considered a match in North America. If it doesn't work, contact Samsung or send feedback to Google [via Settings - just put feedback in the search bar and give them the "A 0-9 ..." sentence above in the feedback. I don't get a +1 on my incoming calls, so I've never had the problem, so I never sent them feedback. If it already works (and I can't check it), sending them feedback would be stupid.
Although Google will probably say that Samsung has to do it individually for each of their CSC (Consumer Software Customization) setups.
(If anyone asks you to do the regex for them, it's \+?1?<then the area code and number>