Phorurex has way more counters than deer. The only true deer counters are grypo and maybe indot; it swaps out on everything else (usually into scorp g3, which counters all of the other deer counters). Phorurex is countered by spyx, trebax, skoona, testa, antarc, lux… plus magnus, monolorhino, compsocaulus, and spinoconstrictor can really hurt it, if not fully kill it.
I’m running phorurex on both accounts, one in high library/low gyro (level 30, half boosted) and one in high gyro/shores (level 30, fully boosted). I’m meeting a lot of other phorurex, too. Sometimes I am destroying two team members with it; sometimes I’m getting destroyed by spyx or lux or even dio. Sometimes one is taking out a couple of my team members; sometimes I’m one-shotting it with trebax or bullying it with resilients. It hasn’t been a huge problem so far either way.
Indotaurus (which I also have at 30/30) is even harder to get a couple kills with, btw. I wouldn’t call it OP by any means. Most people actually consider it the inferior carno hybrid to scorp g3.