Why does she need to get phone numbers of every guy she meets?

So I've been dating this wonderful girl for about a year now. Recently, she's been chatting with guys online and in person and getting phone numbers from almost every one of them.
She's told me I'm "the man of her dreams" and I thought we were happy together.
Why the hell does she need this constant attention from other guys? It's really starting to piss me off.
I've called her on it and she says it's nothing but I'm very skeptical. If it were some random guy, whatever. But it's almost everyone she meets.
Am I overreacting or is she doing something really wrong? And how can I get her to stop?