2005 sebring. does it have valve in gas tank neck

That's just a spring loaded flap that is designed to keep gasoline vapors from escaping for the instant the gas cap is off. It just pushes out of the way for the gas nozzle when refueling. So if you want to pour an additive into your tank, just use a long skinny neck funnel or just push the flap open with a screwdriver. Touch the car with your hand to discharge any static spark before touching gas fill spout with a (metal) screwdriver or metal funnel.

thank you. is there a screen on fuel pump. what I am finding, says there should be.

Yes, all fuel pumps have a screen that prevents pieces of stuff getting drawn into the pump and breaking it. Don't worry if you drop something into the fuel tank. It won't go anywhere, just make sure it's not a diamond ring. Outside the tank along the frame/body rail there will be a filter that's replaced about 30-50K miles.