Learning English as a foreign language is bedevilled by the existence of verbs whose meaning is contained in more than one word, for example 'to be fed up with'. This is a group of words with a single meaning - it is a 'lexical unit'. It is not simply to be understood by taking the word 'fed' (the -ed participle of 'to feed') in the passive voice, and the prepositions 'up' and 'with'.
Often, a phrasal verb's second element (after the verb) is a preposition. Here, it needs a complement. "He came across a solution to his problem", for example; the preposition 'across' needs a complement - here 'a solution'. Hence the term prepositional verb is often used.
But other phrasal verbs consist of a verb and some other element. This is most usually an adverb (or an adverb particle). We 'think ahead', for example; or 'look back'. Sometimes such a phrasal verb is followed by a further preposition introducing an adverbial phrase - we might 'look back on the past', or 'think ahead to next year'.
This is another distinction best left to those with an interest in the theory of grammar. For the purposes of a working, everyday knowledge of the subject, it is best to think of all constructions where a verb with a particular meaning consists of more than one word as phrasal verbs. Leave the subtle distinctions to others. (And don't confuse phrasal verbs with verb phrases.)
Note on terminology: Phrasal verbs consisting of a verb and one additional element are sometimes referred to as two-part verbs, and phrasal verbs consisting of a verb and two additional elements are sometimes referred to as three part verbs.