By default in Sphere, all donations cannot be made automatically anonymous.

However, you can set the field default text to show anonymous instead of being blank. This will allow donors to change the name if they as well if they desire to. Note: Donations that accept credit card information will still access the donors name since credit card transactions will utilize the name that was entered in the Billing Information section.
In addition, it is not recommended to allow all donations to remain anonymous due to the chance of records being merged along with the difficulty in searching for specific records.