Then it sounds like you need to practise settling without visitors around.
If you have a doorbell, disable it/change the noise and ask visitors to knock. If they knock, get a doorbell. He's already attuned to the current noise and knows it means guests, so you need to change his association with the door iswyim.
Then, you need to work to desensitise him to the (new) sound of the door. When the door goes, he needs to do what you ask - stay in his bed, go behind a baby gate, go in another room (whatever you want him to do). This will take a LOT of repetition to get right, but eventually it should be automatic.
Then you add visitors into the mix. So, door goes and he stays in his bed/goes behind a baby gate. He has to stay there (calmly) until visitors come in and sit own (get someone to wait with him to keep in his place via treats or a lead).
Once visitors are settled and the dog is calm, let him in - get them to chuck the treats down at the dog, avoiding eye contact and not giving him any fuss. This should stop the dog jumping up and being silly. As long as the dog has all four paws on the floor, allow guests to greet. If he jumps up, they need to ignore him, fold their arms and avoid eye contact until he's calm.
It will take a lot of work and repetition at first, but eventually he should get it. Cockers are smart dogs, after all.
Another option for now is to take him outside on a lead and allow him to greet guests in the garden, get the initial excitement over, then bring him indoors with them.