Phosphate tests are notoriously inaccurate because phosphate only stays in the water column for an extremely short period of time before being consumed by algae. If you've got dinos, you've got a phosphate/nutrient problem, regardless of what your test tells you!
Are you using RO/Di water? If so, when did you last change your filters and are you using a TDS meter?
How much, how often, and what types of foods do you feed?
How many fish do you have, what do you have for a clean up crew, how much live rock do you have, and what is the size of your system?
Answering all of these questions will help us narrow down the source of the problem!