I will not keep it in the freezer. Most of the time, you will need to transport the milk back at the end of the day in your cooler bag. If you put it in the freezer and it gets frozen, it might thaw a little on the way home in your cooler bag. Then you can't refreeze it again. Chilled milk can last for 48hrs if they remain chilled. So you can use the milk within 48hrs when you reach home. My advice would be to feed your baby with milk that you pump in office, and for milk that you want to freeze and build up your storage stash, you can use milk that is pumped at home.
I store in the chiller, with the icepack on top and pack all into cooler bag to transport home. Avoid freezing it as it will start defrosting on your way home.
I use cooler bag/ chiller with two frozen ice pack inside. Can last frozen for 10 hours
Just the fridge will do or cooler bag with lots of ice packs.
thanks