Like it says in the name, phrasal verbs are verbs, but not just any verbs they are verbs with a particle, either a preposition or an adverb, or multiple particles.
English has many verbs with for example a preposition:
The list goes on.
But unlike the previous examples when you take the verb and you add a preposition to it the meaning changes.
look + at = still means you are looking at something.
Look + after =
doesn’t mean you are looking behind you. It means to take care of someone or to provide for or keep something or someone safe. For example I look after my children when my wife goes to work.
So, there you have it. Phrasal verbs are verbs which have a different meaning than that of the original verb.