I learn from Oxford English Grammar Course:Advanced by Swan that verbs with adverb particles are often called Phrasal Verbs.
An example to illustrate my confusion, I'm doing the exercise about determining whether the given sentence is using preposition or adverb particle. This is one of the sentences:
I looked up the street to see if Andy was coming.
The answer key told me it's a preposition, but I found the phrase look up listed as a phrasal verb in OALD which means to raise your eyes when you are looking down at something. I also ever read somewhere that phrasal verbs are just verbs + prepositions. Does that mean each author might have different view? I'm pretty sure I've read that, but I can't tell where, I don't remember.
Related to the title, so how do you tell precisely if the small word that comes after a verb is preposition or adverb particle? For example, an English learner might not be able to tell which one is verb + preposition and verb + adverb particle:
He got off the bus.
I switch off the lamp.
I took those examples from the book I've mentioned above. The book says  is verb + preposition and  is verb + adverb particle. I'm hopeless if I have to remember one-by-one and start to memorize which is preposition and which is adverb particle.