The electric dipole contain two equal and opposite charge. So total charge is zero inside the sphere. Apply Gauss's law, the flux,ϕ=Qenϵ0 where Qen is the charge enclosed by the sphere. i.e Qen=0 so ϕ=0.
The electric field is the resultant field effect due to all charge. So the filed is not zero inside sphere or any other point on the sphere.