I'm not going to let my girlfriend look at my phone.
Why would you not let your girlfriend look at your phone?
It contains private things that she shouldn't see.
I know that you want to keep some things private but you shouldn't be hiding things from your girlfriend. If you're ashamed of the things on your phone maybe you should just delete them.
She will leave me like my ex girlfriend if I show her the things my phone.
So, maybe you should reconsider the deletion. I guess you learned your lesson as your last girlfriend left you for hiding things on your phone.