I can put my in-ear hearing aids into telephone mode, and they become partial ear plugs to external sounds. Of course without wires people still assume I can hear them speaking, but it does reduce unwanted ambient noises for me.
Phones, including cell, are hearing-aid compatible, which means they emit a short-range electronic signal the hearing aid can convert to sound internally. So in that mode I can be in a very noisy environment that I barely hear acoustically, the hearing aid sound pickup being muted, but I still hear the telephone speech clearly, allowing me to take the call. Of course the other person on the line may have trouble making me out, because my own voice may be competing with the noises surrounding me.