The first 3 digits, i.e. the ones between the parentheses in your example, is called the area code.

Area codes in North America were divvied up by US and Canada, and they share the same phone number structure.

Older area codes tend to have a "1" or "0" in the middle, but that convention went away, as devices like fax machines(!) and mobile phones proliferated, and more numbers were needed to handle the load.

The various telephone companies coordinate through the North American Numbering Plan (NANP)

A list of area codes and where they're supposed to be assigned to: https://en.wikipedia.org/wiki/List_of_North_American_Numbering_Plan_area_codes

I say "supposed" because you can take a mobile phone number anywhere these days.

The 2nd 3 digits, e.g. "745" in your example, traditionally meant a certain area within the area code. So for example, phone numbers in the 613 area code having 2nd 3 digits of "743", "744" and "745" would typically be to addresses near each other.

That might designate a specific city, or a group of towns.

Once again, mobile phones have taken some of that meaning away as landlines are disappearing.