You need 18 chars to enter Belths room. to use the teleporter.
But first yes teleport to Beleths Mutated Elpy. After you kill the elpy spore mobs will spawn. I believe it takes 200 kills for Epidos to spawn. If you run out of mobs kill the elpy again and kill more mobs. Epidos will spawn. After you kill Epidos the teleporter will spawn.