ARS picks the most exact match. That said, I've only tried that without x's as wildcards. Like 1855976 is more exact than 1855. I'd reckon that 1855976 is more exact than 1xxx976.
The basis of all that is NXX 976 was traditionally reserved for pay per minute calls like 1-976. There's countries in the North American number plan that use area codes. So, you call Jamaica as 1-876 and probably not with a 011 leading.
Good old fashioned scam is to get people to call a foreign country as a 900 type call, hence why it's blocked by default in ARS.