What is the difference between the phrases "lose touch with reality" and "out of touch with reality"? And can I use either of them to describe people who are addicted to video games?
Lose touch with reality implies you were once in touch with reality.
Out of touch with reality is silent on whether or not you were ever in touch with reality.
can I use either of them to describe people who are addicted to video games?
Just because someone feels an overwhelming need to play computer games doesn’t mean they’ve lost touch with reality.
Also, addict is often used in a non-medical way (especially with respect to pop culture), so a video-game addict might just be someone who enjoys playing video games a lot, but doesn't meet the clinical definition of addiction.
However, if your assertion is that in some cases someone is so obsessed with computer games that they simply no longer have any regard for the real world, then you could probably use it. But that would be an extreme case.
What is the difference between the phrases "lose touch with reality" and "out of touch with reality"?
The difference is in the verbs. 'to lose' versus 'to be out of'.
the state or fact of being in contact or communication or of having awareness
We could say (or presume) that the usual state of most people is to be in touch with reality. That is to say that they have a rational understanding of the world around them.
"to lose touch with reality" means to lose that connection with reality.
"to be out of touch with reality" means that you do not have that connection with reality.
The first is a progression from one state to another. The second is one of those states.
The same difference as between, "to lose X" and "to be out of X" whatever X happens to be.
I see that Graham Nicol has answered at roughly the same time. I partly disagree with Graham. I think either phrase could be used about people who are addicted to computer games. There are degrees of losing touch with reality. The most extreme would be to be unconscious or dead but, for the phrase to be useful, we must allow other levels.