It's 407-WDW-CAST, but the last time I tried using that number they were making everyone use the portal to initiate the reservation, and the number was only to make changes or to use if there were other issues.
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Yep, and now you can also do WDW Dining Reservations on there too. Indeed, you need to if you want to get the Cast Discount.
These days, you only need to call the Cast Line if you're modifying something that you can't do on The Hub, you're booking something special (ex: large parties), or if The Hub is being it's "normal" self and giving you problems.