O=P1(O)Oc2c(c(-c3ccccc3)cc3ccc4ccccc4c23)-c2c(-c3ccccc3)cc3ccc4ccccc4c3c2O1
A rotatable bond is defined as any single non-ring bond, attached to a non-terminal, non-hydrogen atom. Amide C-N bonds are not counted because of their high barrier to rotation.  How many rotatable bonds does the molecule have?