It's not a phobia or a fear of relationship at all, if you think about it...it is just our rational mind acting up. In a relationship, rational thinking doesn't work, if both thought that they think rationally, they shouldn't spend too much money on going out...sooner or later, things will get boring and the "flare" of the relationship will deteriorate into just a concious problem, fearing that you might hurt the others feeling and thus force yourself to be trapped into this loveless relationship. If rational thought plays up, it'll mean that you just don't want to be trapped in a loveless thing in the future.
And also, to be honest, nice guys aren't what girls are looking for, at least not at this age, nice guys will often say yes to everything (i even admit i'm like that) and will probably end up being a rebound guy at best...it's just how life is...nice guys are the ones who most often truely love the girl, but will most certainly not be a young girls first pick, but will be something that girls regret letting go...
Young girls most often want someone who is fun, lively, and can associate with others, and certainly a confident person...someone who can make them worrie, and angry...because think about this, if you get angry at someone, you will remember them more vividly
So don't worri, it's not a phobia, it's just human nature especially nowadays, to think of themselves before going blindly into a relationship. Remember, if you love someone, you would never think of fearing the split up even before entering it...forget about hurting someone, and just enjoy yourselves, irrationality is what defines true life enjoyment, ever done something that you thought later "damn! i was lucky not to get killed there"...and then you're pretty happy because you survived...if you thought rationally, that wouldn't happen in the first place...if you don't agree, blast me!!
Damn!! that was a long post....