Change Listen 80 to your desired port xxx
sudo nano /etc/apache2/ports.conf
#Listen 80
Listen 8888
Make sure your VirtualHost also listens on your desired port xxx
sudo nano /etc/apache2/sites-enabled/000-default.conf
From port 80 to xxxx
<VirtualHost *:80>
<VirtualHost *:8888>
Now restart apache2 service
sudo service apache2 restart
Verify listening ports
netstat --listen
netstat -l