We can access the SharePoint sites from mobile devices by using mobile browser or rich client application. To access the site from external devices we need to enable external access. We can configure the external access in three methods,
Reverse proxy server: In this method, reverse proxy server enables us to publish the SharePoint sites on the firewall. To do this we need to configure the reverse proxy server and publish the SharePoint site in that reverse proxy server. After publishingthe site collection , we have to configure the alternate access mapping to the SharePoint site. We have to add that SharePoint site to a zone that allows the cross-firewall access. We configure the cross-firewall access by using the steps below. We need to have the farm admin access to configure the cross-firewall access zone.
Navigate to System Settings in SharePoint Central Application.
Select “Configure cross firewall access zone” in System settings page Farm Management section.
Select the web application to be published the firewall in Cross Firewall Access Zone page Web Application section.
Select the zone that to be published across the firewall in Zone selection for cross firewall access list in Cross Firewall Access Zone section.
Mobile proxy server: Mobile proxy servers pass the mobile browser access directly from SharePoint 2013. This method helps mobile devices work within company IT infrastructure.
Direct access through internet: Here we can place the SharePoint site in extranet and we can access the site by passing the URL directly. Only basic authentication supports this method. Using policy safeguards with the combination of technology is recommended in this method.