An iPhone 4 is 4.55 inches tall. The 'mushroom' top you're talking about is normal, if you have been circumcised it's always visual. Anyone who's circumcised it's always visible. If you aren't circumcised you have foreskin, and the 'mushroom' top is under the foreskin. You're still going through puberty, so your genitals will continue to grow for a few more years. Don't worry about any of this right now, you're thirteen. Honestly, don't ever worry about it unless it's affecting your health. Girls will like you for you, if they don't, and worry about how you look down there, they aren't the right girl.