The thing is... it's still carbon, and as such won't do you much good after a couple weeks. The Phosguard part of it might be still working for you, but the carbon will be shot. But because the stuff is mixed, you can't just replace the carbon so you end up replacing everything and throwing away perfectly good Phosguard.
Personally... I steer away from any aluminum-based phosphate removers (like Phosguard) and use GFO
(granulated ferric oxide) instead. I also use Purigen (another Seachem product) instead of carbon. You can regenerate Purigen, unlike carbon. I'm not sure I really get any more useful life between changes using Purigen over carbon - even though the literature would have you think different - but the fact I can regenerate Purigen makes me come out ahead in the long run. And I run them in separate bags, so my hands aren't tied as to when to replace them.