Your spike is very early in development. You could repot this orchid without much worry. When we were selling phals commercially, we would buy phals from Hawaii that were just about in the state of the one in your photo. When they arrived here, we would repot them, spray them, tag them and then sell them when they bloomed. We never had a problem and the only thing we did was be careful not to disrupt the roots too much.
If you still do not want to chance it, you could spray and run some insecticide through the medium. That should end the gnat problem. Also, keep a fan blowing on the plant to move the air around. They (the gnats) will hate that.