So my girlfriend seems to always invite her friends to join in on OUR time?

My gf always talks to her friends and it's not that I don't like them, because I do. However, she never asks or includes me in any of the plans while she is on the phone making them. It's as though she just assumes which seems a bit disrespectful and self centered. I've expressed my feelings about this more than once so I'm not exactly sure how to deal with it. I feel almost taken advantage of and not respected in the relationship.
So my girlfriend seems to always invite her friends to join in on OUR time?
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