This is called a lookahead. Parentheses Create Numbered Capturing Groups Besides grouping part of a regular expression together, parentheses also create a numbered capturing group.
If the multiline flag is set to true, also matches immediately after a line break character. You probably know about capturing parentheses. The non-capture group? Notice that the entire phone number match is in match. Typically, this would be used in a case where you want to capture something on each line, except those that present certain features.
Only parentheses can be used for grouping. Even so, I was still surprised when I learned that there are 3 different kinds of parentheses in regular expressions, not just 2.