IME you've really got to go with your gut. Each woman is different. Younger girls tend to be more fickle and play more games. Older women tend to appreciate the thoughtfulness a bit more, but take things more seriously.
If you think she's not thinking about you, you are probably right. Ideally what you will get is telephone reciprocity even early on. You call, She calls, you call, she calls and so on. If that doesn't show up, she's either seeing someone she likes better or she's super old-fashioned.
I really think you can't go wrong just being straightforward and honest. Treat her like a friend you are planning to meet up with and make the normal amount of contact for that. I think it is in the man's interest to not get into lengthy phone conversations unless she initiates. Even if it feels weird, it's important to make yourself in demand. Always be nice, always be courteous, always be responsible, DON'T be easy.
Good Luck. I wish I was having this problem right now.