It is never easy for two persons of different backgrounds and upbringing to come together as lovers - hoping to form a family. So it takes a lot of effort for the two to live in harmony and love. However, this can never be achieved in the absence of trust. Trust is the building block of any relationship.
Going through a partner's phone is surely an indication of a lack of trust in the relationship. For a relationship that is built on trust, it is rare to see such happen, however, it only occurs when one's partner starts being suspicious of him.
With the way we are attached to our mobile phones, the easiest way of catching a cheating partner is through the phone. And such a person would do anything to protect his phone from his partner. And that's why refusing your partner access to your phone implies that you are hiding something - in fact, you are cheating.
For me, allowing my partner to go through my phone isn't a big deal. In fact, my partner has access to my phone. But what I have issue with is when she starts reading meaning into my chats or other things. And that's why I am a big fan of good communication among lovers.
Establishing excellent communication with your partner goes a long way in curbing the issue of distrust. Letting her know how your day went, the challenges you experienced, and other things help a lot. With this, it would be rare for her to start going through your phone.
Lastly, privacy is also needed in a relationship. Some things in the past are better left in the past. It is not also advisable to be intruding into your partner's space. However, too much of everything they say is very bad.