If I erase all my content and settings/data on my iPhone 4, will it erase my number too?

I need to erase everything to make room for an update but for that I need 4.7 GB and I have 4.4 right now. I deleted and backed up everything I could but I for some reason can't delete my mail even if I sign out and I just can't lose my number

No… Your number is on your SIM card.