to build up: to increase slowly, to make stronger gradually Examples of TO BUILD UP They certainly have built up a vibrant user community in a short period of time. These deficits have been built up over the past 10 years and nobody said a peep.  

to be up to: to be responsible for deciding; to be doing as a regular activity Examples of TO BE UP TO I can tell when you’re up to something, but I don’t know what yet. Sam is always getting up to trouble.

to cut down on: to reduce, to lessen (also: to cut back on) Examples of TO CUT DOWN ON As she was making her budget, she realized she needed to cut down on her expenses. My doctor told me to cut down on desserts.

in time to: before the time necessary to do something Examples of IN TIME TO He had good position but had not turned his head in time to see the ball arrive. Officers went to the hospital, but did not arrive in time to talk to the victim.

on purpose: for a reason, deliberately Examples of ON PURPOSE “So you’re telling me that you lost the game on purpose?” the commissioner asked the baseball player who was accused of taking a bribe. I tried to explain that the boy didn’t break the window on purpose, so his parents wouldn’t be mad at him.

to put out: extinguish, to cause to stop functioning Examples of PUT OUT I decided to put out the light and go to sleep. We hope to put out a deluxe edition of the award-winning novel later this year.