I don't know if this will be the correct number you are looking for but i found this one online for Disney's lost & found.
Yup, that's the number alright. Operating hours are 9am-7pm 7 days a week.
Keep in mind that each hotel has a lost and found and downtown disney has a lost and found. The number above is for the resorts. After each day the theme park sends their lost & found items to the central Lost & Found which is located at the Transportation and Ticket Center in the Kennel Club Building.