This is kind of difficult.
There are other casual phrases, such as
I like spending time with my friends.
But that is certainly not formal enough.
However, anything formal on that score is almost certain to come off as mockery. Consider:
I am very fond of social engagements.
Socializing is one of my hobbies.
Mingling is one of my favorite activities.
I spend a great deal of my spare time hobnobbing with my associates.
The answer, in my opinion, is
leaving it as it is
OR (this is important!)
skipping it altogether.
Most people like to hang out. It is not one of those unique traits that could automatically pique an objective reader's curiosity.
Last but not least, mentioning that you're sociable might come off as a bit ambiguous.
This, of course, is merely my opinion, which I hereby encourage you to ignore.