Every eigenstate of the hydrogen atom, once you have specified the r and θ dependence, multiplies the resulting function by eimlφ.
Note that |eimlφ|=1 for any values of ml or φ. So if the electron is in an energy eigenstate, the position probability |ψ|2 will be multiplied by 1 for all values of φ, having no effect at all. Therefore, |ψ|2 will be the same for all values of φ; in other words, the position probability will not be a function of φ, implying rotational symmetry about the z-axis..
On the other hand, in a combination of different eigenstates with different values of ml, you multiply each eigenstate by a different eimlφ. They will constructively interfere at some places and destructively interfere at others, giving different position probabilities at different φ-values.