You should definitely contest this ticket, because you were not "us[ing]" the phone. Also, if you were hitting [send] or [end], you are specifically exempted from violation (See below). The statute reads as follows:
§ 50-1731.04. Restricted use of mobile telephone and other electronic devices.
(a) No person shall use a mobile telephone or other electronic device while operating a moving motor vehicle in the District of Columbia unless the telephone or device is equipped with a hands-free accessory.
(b) The provisions of this section shall not apply to the following:
(1) Emergency use of a mobile telephone, including calls to 911 or 311, a hospital, an ambulance service provider, a fire department, a law enforcement agency, or a first-aid squad;
(2) Use of a mobile telephone by law enforcement and emergency personnel or by a driver of an authorized emergency vehicle, acting within the scope of official duties; or
(3) Initiating or terminating a telephone call, or turning the telephone on or off.
