several test kits contain tests for phosphates. On the iodine test kits, a few companies make them, but generally they are difficult to read and only test for certain ionic forms of iodine.
Are they as important as the nitrogen cycle? In some ways, yes....phosphates can impact algae and cyanobacteria populations, so maintaining low phosphates is a good idea. Iodine can be bad if overdosed. However, normal feeding and water changes usually provide the reef tank with plenty of iodine, making supplimentation and testing for it unecessary in most cases.
MikeS