ZenMate secures and encrypts all web traffic on your phone, whether you are using a mobile browser or any other app that connects via internet.
It does not protect your phone calls or SMS since these are not sent via internet. But if you use a VOIP app for your phone calls, those calls will be encrypted of course.
While ZenMate encrypts all traffic entering and leaving your phone via internet, information that you enter manually into an app (e. g. WhatsApp or any mail app) also passes through an unsecure host server out of ZenMate’s control before being routed to the recipient. In general, it is important to remember that anything you transmit over the internet is not 100% safe.