1. Your partner is not ready for a serious relationship.
If your partner prefers checking your phone behind your back over actually talking to you, this might be a sign that they’re just not mature enough to be in a relationship. They can explain their behaviour this way — they just want to know who called you and that’s all, no jealousy. But, instead of playing hide-and-seek on the phone, they could just go straight to the source and ask you directly about it.
If a person can’t ask you such a simple question, imagine how they’ll feel when you need to talk about more serious topics, like moving in together or planning a family. So, they’re probably just not ready to build a serious relationship at this particular time.