My phone is saying unknown camera part and I have not had any modifications made to my phone. Why is this happening?

That message came in three different things

• Was replaced with a nongenuine camera
• Was already used or installed in another iPhone
• Isn't functioning as expected

If it’s not showing a service history per iPhone parts and service history - Apple Support then it’s likely the third reason above. This is just a generic hardware failure message and you’ll want to get the phone in for repairs.