You can use port forwarding inside your Vagrantfile and map port 80 from your host to 80 from your guest:
config.vm.network "forwarded_port", guest: 80, host: 80
If your apache in your vm doesn't run on port 80, you need of course change the guest port.
BTW: Running vagrant on DigitalOcean doesn't make much sense. Not sure why you need it, but vagrant is designed as a development environment running on local machines.