Spawns at 2507, 921, -194 (deep underwater by the base of the aviak ramp that also has the flame of innoruuk; on the island east of the Arena ZL).
Pic By: Gestahl Ghoulblight Guardians of Darkness
rja69 gives the following based on Phinigel Sever progression:
1) you need to make sure he, or a PH is not already up and swimming around. This is the toughest part. His PH can be almost anything: alligator, shark, aqua goblin, froglok, or piranha sure about the piranha. Find it and kill it. For me, I found that the gobs would tend to swim west from spawn point then circle counter clockwise. They swim fast, you'll want sow/jboots.
2) once the PH is killed, go to precisely this point: 2046, 749, -49. Adjust your depth so that your clip plane gives you the most distant view, so your eyeballs are right at water lvl.. any deeper and the underwater fog creeps in.
3) Face exactly east.
4) Every 2-3 minutes something will spawn nearby. I believe the actual spawn point is due easy of the point I mention above, but stay where I said and watch due east. Pet up if you have it, or use ranged weapons. Use SHD Track skill (i.e. keep hitting your Tab key, or whatever you have to lock on to nearest mobs) until you lock on to something, then, without moving, kill it (pet or ranged.) If it's not in range then it has spawned due east and is swimming towards you. Wait for it then kill it.
5) I killed everything that spawned nearby, even the stuff that spawns north and south (mainly fish, snakes, and occasional piranha). I'm not convinced that these nearer spawns are PHs, but why take chances?
If you do all the above, Webclaw will eventually spawn due east swimming towards you.