I think there are a couple problems here in the way you are been talking to your girlfriend about her jealousy.
First, there seems to be a bit of a communication issue. When you say "None of these girls are into me", your girlfriend hears, not entirely unreasonably, "Fortunately, none of these girls are into me, otherwise I would be tempted to cheat on you." When you tell her "not many girls are into me" that also rings very false to her because she obviously thinks you are a good enough catch to be jealous over! (Kind of flattering, right?) I think you are unintentionally placing a lot of emphasis on the idea that you don't currently have a really good opportunity to be unfaithful, and that is sending a wrong message that feeds her insecurity, although it's really not what you mean to express.
When you talk about how you spend time with other girls, it might help if you leave their qualities/interest in you/behavior out of it. This conversation is really about you and your girlfriend, and not anyone else. Even if the girls are interested in you, or even if they are promiscuous or regardless of how they think or behave, that doesn't matter because you are in charge of your own actions and have decided to be faithful. That's what you should focus on as far as trying to reassure her. Words like, "I made a commitment to you, and I care about keeping my promises to you" tell her a lot more about why she should feel confidant in your relationship and your character compared to, "Not many girls are into me". In cases where I or my partner have been jealous, a direct affirmation of our commitment has gone a long way to soothing the insecurity and jealousy.
Secondly, you might what to revisit what happened when your girlfriend brought up texting. If texting while you are with friends is something you are not willing to do, that's a perfectly reasonable position to hold and you are well within your rights to tell your girlfriend so. You can set a boundary around not using your phone when you are with friends if that's what you want, but do it because you need phone-free time with friends or you want to avoid being rude (or whatever your need is around this), and NOT because she is delusional/crazy/unnatural. When your partner says, "I need this from you to feel more secure in our relationship" the response, "That's crazy and I shouldn't have to do it" is not constructive, and even a bit unkind.
Of course, this is not to say that you are the bad guy in all this and your girlfriend's behavior is fine! Spending time with your friends without your partner being excessively jealous, suspicious or untrusting is a really reasonable thing to expect in a relationship.
It is definitely discouraging when someone you care about seems to hold a deep belief that you are just waiting for the opportunity to be unfaithful to them, and this is definitely something you should talk about with her, and an area where it's fair to expect her to change her attitude.
Either way, any conversation where one person starts from the position, "I don't have to change at all, there's something wrong with YOU" is likely to go badly. Starting with a focus on your own needs and feelings is usually a better way to start. I try to use this pattern when I have to have a tense or difficult conversation with someone I care about, and it generally leads to some kind of positive compromise. In this case, you may say that you feel sad that she doesn't treat you as a trustworthy person and you need to be able to spend time with your friends and have your own social life (or whatever better describes your situation), and that you need her to extend a little more trust in you and stop making accusations about you being unfaithful.
Then ask her what she feels about the situation and what she needs. My guess is that her feelings are going to be one of more of the following: left out of your life, lonely, less important than your friends, scared of losing you, forgotten, insecure about her worthiness in your eyes. Whatever her feelings, they may not make sense to you, but that doesn't make her wrong or crazy. What she needs might be to feel included with your friends, reassurance, or something else.
Then, you can ask her to work with you to find a way to meet both of your needs. Maybe she really just needs to be told that she's your number one more often. Maybe you can send her a text once as you're on the way home from seeing friends, but not plan to chat the whole time. It's less about finding a way to make her stop being jealous, and very much about working together so that you both have your needs in the relationship met in a reasonable way.