I feel I'm probably missing something obvious, but how do I make a phone call from my iPhone using my watch? I'm not wanting to start it on the watch and handoff to the phone. I just want the watch to make the call using the phone.

When out walking the dogs I've got my phone in an inside pocket, and am listening to music via bluetooth headphones. I just want to be able to make a call from the iPhone without having to get it out of my pocket. Is this possible?