These are not common ways of describing this kind of grammar, so I'm not surprised that you're confused. A phrasal preposition is a phrase that works as a preposition, eg. "instead of", "with regard to", "out of" and so on. A prepositional collocation is when a preposition naturally goes with a certain noun, verb or adjective, eg. "excited about", "provide (someone) with", "a lack of", "make contact with", "get married to (someone)" and so on.