You can test it for phopates with a phosphate kit. I think that some of the LFSs will test it for you. If I were you, and worried about it, I would just use the chemi pure.
The stuff you have might sitll work, but I would put some in a filter bag, or womens nylon for a cheaper version, and soak it in some RO water for a day. If anything is going to leak out of it, it will happen during that time.