Yes, ‘in addition’ is considered a prepositional phrase.
A prepositional phrase typically consists of a preposition followed by a noun or pronoun, which acts as the object of the preposition. In the case of ‘in addition,’ the word ‘in’ is the preposition, and ‘addition’ is the noun that serves as its object. Together, they express the idea of adding something to what has already been mentioned.
For example, you might say, ‘In addition to studying, she also works part-time.’ Here, ‘in addition’ introduces an extra piece of information, showing that there is more to the situation than what was previously stated. Thus, we classify ‘in addition’ as a prepositional phrase that enhances the meaning of the sentence.