Can you take your phone with you on the rollercoasters if its in a zipped sweatshirt pocket.

Simply yes. Lol

Many rides have compartment next to the ride operators where you can put your stuff. They are marked according to train and they are locked between trains. On some of the rides I actually had my phone out recording videos while I rode. Check the weather because a sweatshirt might not be the best idea to bring with you or wear while there. I wore cargo shorts and a t-shirt and my phone and wallet were just fine

Yes

Cedar point has now added zippered pouches under all coaster seats to put any loose items in.

Yes if secured your good

Yes you can.