function clickButton(obj){
    var obj = $(obj);
    obj.attr("disabled","disabled");
    var time = 180;
//設定倒計時以毫秒進行計算，1000毫秒後減1
 var set=setInterval(function(){
    obj.val(--time);
    }, 1000);
    setTimeout(function(){
    obj.attr("disabled",false).val("獲取驗證碼");
//取消setinterval當180000毫秒以後
 clearInterval(set);
    }, 180000);
}


<div class="col-sm-4">
  <input class="btn btn-sm" id="verify" type="button" onclick="clickButton(this);" value="獲取簡訊驗證碼" />
</div>