Some words have different parts of speech that are identical to each other. For example, "out" can be accompanied by a verb or it can be a preposition or an adverb. How to differentiate these parts of speeches?
You also need to know that writers are not always in agreement on this.
Allow for, for example, is called a verb + preposition in one of my books, a prepositional verb in another, and a phrasal verb in a couple of others.