What part of speech are the words in the phrase “as well as”?

In the sentence:

My car as well as my lap top were stolen last night.

What part of speech are the words in the phrase as well as?

I believe the first as is the preposition of the phrase, that well is an adverb, and that the last as is again a preposition. But I am not sure.

Or do the three words function together as a syntactic element? If so, what would that be called?

In the example you have provided, as well as functions as a coordinating conjunction replacing and. See:

• They stole my car as well as my laptop.

• They stole my car and my laptop.

The entire phrase is a synonym for and.