Is he still looking for more food after he's finished or does he leave some behind?
You could always supplement the pouch/canned with bits of cooked chicken, turkey, beef, lamb, scrambled eggs (low phos high protein) if he'll eat them.
When I was started feeding raw there was actually slight drop to Duffy's phos counts, hers fluctuated a little bit but were never above mid-normal so I wasn't too concerned about phos levels.