I just want to know, I just want to do it safely. My phone always said it's almost full storage but I did delete all my text messages, pictures, apps, etc. I tried everything but it always said the same thing. So I don't know if I erase the content and setting will help me erase some parts in my iPhone 4s. I'm trying to make sure.
No, your phone number will not be affected.
Your phone number will not be affected.
But try to see what is occupying the space with "Settings -> General -> Usage.
Back up via iCloud or iTunes then go ahead and delete stuff.
Look for apps that use a lots of space and delete them "Delete App and Delete App again to confirm.
Your messages can contain a lots of photos send to you that consume space.
If you are unsure if you want to keep some you need to "Manually Find & Save Photo Messages".