Yes I've broken up with people because of my anxiety and I haven't maintained friendships because of it sometimes too.
Your friend should be more understanding and not reprimand you for needing space. But it just shows you how much you mean to her if she wanted to talk to you so badly and you weren't answering your phone.
Its okay to need space sometimes. Lots of people, as they get older, end up not having many friends because work or family life takes over instead. I don't know of many older people who have active social lives, I could be wrong here...but its just something that happens with age anyway. Now being younger, of course your friends might hound you more to hang out or call, but you should never feel obligated or pushed to do something.
Do whatever feels right to you in the moment.