US Law only requires that you enter the amount of people living at your residence. The census does NOT require you to enter anything beyond that. If you are dumb enough to enter your phone number, race or anything else and expect it not to be used against you in some way, then it is your own fault. Seriously, it's like signing up for a website online - they may ask you to enter personal information even though it is not required. You don't see me complaining about those websites asking for my phone number (or anything else that is personal,) and then getting mad when they call me. I deserve the invasion of privacy because I was stupid enough to provide them with my number in the first place. Instead I just don't enter my phone number. Most of the time they don't required that field in the first place; if it is required I would either make it up, or just not sign up.
People that think the government is not going to use this information in some manner are living in a hole. It's the government this is what they do, move on and stop being so naive and think before you blindly fill out anything, because trust me, it is going to be saved and sometime down the road it may, this is not me saying it will happen, but it MAY be used against you.
Be smart, enter the amount of people living at your place, and mail in your census. Problem solved.