Hisoka constantly seeks out powerful opponents to challenge and kill. Razor was acknowledged by the Phantom Troupe to be pretty powerful. Why didn't Hisoka attempt to fight him?
So far (in the anime), the only other fights that Hisoka missed out on were:
Netero -- Hisoka deemed that Netero was leaving himself too vulnerable to attack.
Chimera Ants -- Hisoka was chasing Chrollo.
Chrollo -- Chrollo was cursed and unable to use his Nen abilities.
In the above situations, Hisoka lost the opportunity to fight powerful enemies. For other powerful fighters such as Illumi, Hisoka chose to befriend them temporarily in order to gain something. But in Razor's case, it seems like Hisoka shyed away from the challenge.
Simply because Hisoka has never challenged anyone that are physically stronger than him despite the fact of it's availability. i.e. Uvogin, Franklin, Silva and Biscuit. People who's raw power are way above his. Therefore his attacks are meaningless unless he has more than just bungee gum in his arsenal. Razor has the same build as the characters I mentioned, and is capable of destructive power well above Hisoka's defenses as well(Shown in their volleyball game). Meaning Hisoka does not have the ability YET to pierce through their defenses, unless he has an extremely hax ability.
Rationale: His fight with these people would look the same as Uvogin's and Kurapica's. Unless he has an ability like Chain Jail, there is just no way he could harm them, because they are physically and nen wise more powerful than he is. If he is stronger or atleast at the same level, then that volleyball(not full power) catch wouldn't have broken his fingers. Imagine what Uvogin's fist would do.
Silva - Hisoka can pay the assassin to kill him, and we have a fight.
Buscuit - A dozen opportunities and he does not take it.
Razor - He could've attacked him on the spot after the game.
Franklin - a simple duel between teammates
Uvogin - same reason as Franklin
My thoughts are that Hisoka targets potentially cerebral fights, i.e. people who could give him that must not have that much overwhelming power Chrollo, Killua, Illumi, Ging and Gon.
Also, just to add. Chrollo as evidenced by his fight with the 2 main heads of the Zaoldyecks, did not show any feat basic nen wise that could pierce through Zeno's and Silva's defenses, which is why he used a specialized dagger. Which means in pure combat without Hatsus both he and Hisoka are not in Zeno's and Silva's level and therefore Razor. The only factor that both Zeno and Silva were being careful in their fight with Chrollo is that Chrollo has the advantage of many unknown abilities. Which one of them could possibly be hax, like an ability to put some1 in a cage regardless of their power. Or teleport like we've seen Chrollo did once.
I do think it's pretty similar to what the other answer states in that Hisoka deemed that Razor could and would kill him. On the other hand, Hisoka is really full of himself and he's cunning in battle, meaning he has the capability to beat opponents with higher basic power than himself. He wanted to fight Netero, despite the obvious gap in power, and he wants to fight Chrollo who we all know is also incredibly strong, so maybe under normal circumstances he would have fought Razor. Unfortunately he was helping Gon, and in that process, used a lot of Nen and was injured, whereas Razor also used up his Nen somewhat, so they wouldn't be fighting at full power. I suppose he could've tried to find and challenge him later, but he was trying to find Chrollo after that because Chrollo interests him more. I would assume he didn't want to fight any of the other Phantom Troupe members because 1) A fight to the death which is all he cares about would ruin his chance to fight Chrollo 2) They aren't strong enough for him, which really says something about how he's full of himself.
As for Biscuit... I think she and Netero are doing the same trick. They put off an aura of being no threat to him, which totally curbs his blood lust.