There's this girl in my school,she is my junior and I like her I asked her to be my friend and she agreed,I also asked for her number and she gave me but I don't kow what to talk to her about in phone... please help me I really love her

You talk to her on the phone like you would any friend. That is what she is to you.
"Hi, how are you?"
"What have you been up to since school has been out?"...
Talk about movies or books, music...

Well I'm a teenage girl and my boyfriend just talks a about anything and I never get bored talking to him. He just brings random things up. You can talk about your feelings towards her? You can invite her on a date? Most importantly just try to keep the conversation going, talk about anything.

Ask around on what she likes. Ask her friends, family, etc. With that said, its possible to start a conversation. If she has drama from her side, tell her to let it all out and talk it out with you :D

I don't think you want to start being her dumping ground for drama (if she has any) that gets old and to use her drama to get next to her is tacky.
Friendly conversation, find out what you two may have in common.
Talk to her as a friend, it takes some of the pressure off