Ask yourself this, would YOU hook up your best friend with someone who is unable to treat you normally, like her other colleagues? Garcia's behaviour towards Luke has been childish and annoying, and while Luke is not petty, that may be the reason.
Luke and Penelope get along, she just goes and forth between treating him the way she treated Derek. I believe her thing is that she is still to nervous to grow attachments to someone else. But the whole Phil thing, I’m not to sure. Maybe he thought it would be awkward with Phil technically just getting back to normal. Just saying...
Who cares I'm waiting for them to specifically invent a serial killer or mass murderer that's sole mission is to eliminate Penelope's character PERMANENTLY! LOL! That would be the best episode ever!!! RATINGS BREAKER