What is the function of the phrase "according to" in sentences like "According to my neighbor, it will rain tomorrow"?
It seems like the phrase "according to my neighbor" is modifying the entire clause "it will rain tomorrow." Is there a name for this type of phrase?
[According to my neighbor], it will rain tomorrow
"According to" is not a constituent (syntactic unit).
"According" is a preposition here and "according to my neighbor" is thus a preposition phrase. "My neighbor" is also a preposition phrase, functioning as complement of "according".
The larger (matrix) PP "according to my neighbor" then functions as an adjunct (adverbial), where it is a supplement, or parenthetical, expressing a kind of modality.
Note: Some people prefer to treat "according to" as a complex preposition with "my neighbor" as complement. Whichever analysis is preferred, the function of "according to my neighbor" is the same.