There as of yet no real standard phantoms just as there are no standard calibration tools overall. There are rumors the FDA will make some. Until then below are some publically available digital phantoms:

 

From the private company Maastro

http://www.radiomics.world/?q=node/28

 

From the Image Biomarker Standardization Initiative Reference Manual

https://arxiv.org/pdf/1612.07003.pdf