In order a phone to operate a consumer device, they must have something in common. Consumer electronics is controlled primary over infra-red, and very few (if any) smart phones these days have IrDA transmitter.
In your case, the only common interface seems to be Bluetooth. Whether your DVD/Tablet player can be controlled over Bluetooth - only you, and unknown Chinese genius designing it, know, so you better start from there.
I broke my crystal ball last night, and I cannot tell the make / model of your tablet/dvd player.