flutter textfield 높이 설정 후 내용 가운데 맞춤 불가

Container(
          height: 50,
          width: MediaQuery.of(context).size.width * 2 / 3,
          alignment: Alignment.center,
          child: TextField(
            autofocus: true,
            decoration: InputDecoration(
                //       ，      ，  
                contentPadding: EdgeInsets.all(2),
                hintText: '      ',
                prefixIcon: Icon(Icons.phone_android),
                border: OutlineInputBorder(
                  borderSide: BorderSide(color: Colors.grey[600]),
                  borderRadius: BorderRadius.circular(5),
                )),
            style: new TextStyle(
              color: Colors.black,
              fontSize: 16,
            ),
            maxLines: 1,
            textAlign: TextAlign.left,
            onChanged: (text) {
              //       
              _phoneStr = text;
              print('change $_phoneStr');
            },
            onSubmitted: (text) {
              //    (   )   
              print('submit $text');
            },
          ),
        )