A phrasal verb is a verb plus a small word (up, out, off, in, on, away…) that together mean something new: give up = stop trying, look up = search for information.
Step 1: is it separable?
Separable — the object can go in the middle: turn off the light = turn the light off. With a pronoun the object must go in the middle: turn it off (not turn off it).
Inseparable — the parts stay together: look after the children, look after them. Many verbs with a prepositional particle behave this way (run into, get over, deal with).
When in doubt, the dictionary example sentences show the natural word order.
Step 2: watch the three-word ones
put up with (tolerate), look forward to (await eagerly — followed by -ing: I look forward to meeting you), get on with, come up with. They are always inseparable.
Step 3: learn by particle
- up often means increase or completion: speed up, use up, tidy up
- out often means from inside or to the end: find out, work out, run out
- off often means away or stopping: set off, turn off, put off
- back means return or reply: come back, call back, cut back
The meanings are not always predictable, but grouping helps memory.