Sounds like you want a dialog window.

GlideDialogWindow: Advanced Popups Using UI Pages - ServiceNow Guru

But for service portal you need to use the widget-modal.  Here is something I used to open one.

//Client HTML
<sp-widget widget="data.modalInstance" ng-if="data.modalInstance"></sp-widget>

//Client Script
$scope.openModal = function(ev, table, sysid, query, view){
	
	if(!sysid)
		sysid = -1;
	
	spUtil.get("widget-modal", {embeddedWidgetId: "widget-form", 
															embeddedWidgetOptions: {table: table, 
																											sys_id: sysid, 
																											view: view,
																											query: query,
																											disableUIActions: "true",
																											hideRelatedLists: true
																										 }
														 }).then(function(widget){
		var modalCtrl;
		var unregister = $scope.$on('sp.form.record.updated', function(){
			//Do work here when record updated and then close modal
			modalCtrl.close();

		});
			
		widget.options.afterClose = function(){
			unregister();
			$scope.data.modalInstance = null;
			modalCtrl = null;
		};
		
		widget.options.afterOpen = function(ctrl){
			modalCtrl = ctrl;
		};
		$scope.data.modalInstance = widget;
		
	});
}