What would you do if someone went through your phone without looking? 

Your phone is an exceedingly private place. It’s where your whole life lands. It’s where you correspond with people, where you make plans, where you write down your deepest, darkest thoughts. It’s where you talk smack about others behind their backs, and it’s where you confess secret crushes. If someone has access to your phone, they might as well have access to your full psyche. So it’s no wonder that you would want to keep that to yourself, especially around people you don’t know that well. Even more so in a dating context. When you’re first getting to know someone, there are probably things you want to keep from them. Not in a malicious way, just in a polite and private way. You’re entitled to your own boundaries, and you don’t need to cross them just to keep someone else happy.