Q: Can I set up call forwarding from my Iphone number to another phone?

Not without the phone, unless you contact the carrier and they can help you.

You can, but it's done via iOS, see this -> iPhone: Understanding phone features

Your best bet is probably going to be swapping the SIM into another phone, the calls will goto the phone with the SIM in it, or you can contact your carrier to have them setup forwarding to another number.

Okay, maybe I made an assumption when the OP said the phone was dropped in the ocean that it was lost. However, If it just got wet, then yes, they could put the SIM in another device and it would work.