If you are on old mobile you can craft 3 pheromone darts at a time using 3 ammonite bile, 2 metal ingots, and 1 tranq dart. If you are on other versions you can only craft 1 at a time using the same amount of ingredients.

Also for some reason at least on old mobile they count as "tranq darts" to make more pheromone darts, so you don't actually need a regular tranq dart to craft more pheromone darts as pheromone darts will work.