Measurable phosphate is usually unacceptable.
While 0.5 probably won't harm any livestock, it will cause algae growth. If that's what you want... then I guess I'd leave the phosphates alone for now.
Though phosphates are considered a waste product in a tank, so I wouldn't count on them as a stable, ever present compound... so if you depend on the presence of phosphates... you may be asking for trouble. One day, they may be sky high, and you'll have to do something. Another day, they may be 0.0.