Faking an orgasm

This is kind of embarrassing for me, okay so I'm 15 & my partner and I are slowly getting intimate, we've been having phone sex lately, it's been great and everything..but he always cums, and I try to orgasm but it's not working so I fake it 😔 am I doing something wrong? Why can't I do it? I don't want to admit to him that I can't because it will ruin his self esteem 
Some one help ! Xx