Apple ID is associated with Apple Business Manager

I am new to iOS and just setup an iPhone XR with iOS 12.4. I am not able to sign into the iTunes store on the phone using my Apple ID. It does not give any error message and it does not seem to trigger the 2 factor SMS message. I KNOW the password is correct! I just used the same password HERE and when I use the same password with iTunes, it tells me my "Apple ID can't be use din this store. Apple ID is associated with Apple Business Manager". Surely I don't need to have TWO Apple IDs in order to have an iPhone and to work towards getting an MDM setup for our organization? If so, can you point me to the documentation that I am apparently not finding on how to get started with managing iOS in a small organization?