I want to find a phrasal verb that means pretending to be nice/friendly to someone because you think he/she will help you do something.
Perhaps the phrase sucking up is what you're looking for?
Brad sucked up to his new supervisor, hoping to score a bonus.
It can also be used as a noun.
Jeez, Brad is such a suck-up.
Flattery, or flattering someone, is also a pretty good verb for that. You can also use the phrase butter up.
Brad buttered up his supervisor, hoping to ask him about the bonus.
"Your flattery won't work on me, Brad."
Hope this helps!
Butter up might be the phrasal verb you need. It means
to be very kind or friendly to someone or try to please someone, so that that person will do what you want them to do:
- You'll have to butter them up a bit before they'll agree. (Cambridge)
To Curry favour (with someone) is another option.
Its literal meaning in Old French was "to rub down the chestnut horse", but its allegorical meaning, "to be false or hypocritical" has been in use in English for four centuries, sometimes without the word 'favour':
Falstaff: If I had a suit Master Shallow, I would humour his men with the imputation of being near their master; if to his men, I would curry with Shallow that no man could better command his servants.
Henry IV, Part II