Three possible things.
One, try clicking on the Tailor Pheromones implant itself in the list of implants and see what the Essence value is (the block of data above Essence Consumption). It will most likely say 0.6 for Essence.
Two, if the character has 0.6 Essence or more spent in Cyberware then Chummer is automatically calculating the 50% impact discount for having less Essence spent in Bioware.
Three, if selecting the implant says 0.3 Essence in the data block, or the character has no Cyberware, check the list of qualities to see if the character has the Type O System positive quality. As Tailored Pheromones is a basic bioware implant, the quality will make Chummer automatically treat it like it's Deltaware and cut the Essence cost in half accordingly.