Cloudflare already has an app on mobile devices - but so far it only served your DNS queries. Now the app behaves as a VPN for all your mobile traffic - all data is routed within Cloudflare's network from the moment it leaves your device, which is faster than going through the public internet.
I think it is important to notice that the traffic is first routed to Cloudflare over the public internet, so technically it is not the moment it leaves your device when it starts to get routed inside CloudFlares network and the public internet again soon after in most cases. Being faster crucially relies on having nearby access to their network from your device and from their network to the destination. Otherwise you ultimately just add some additional hops in between, making it likely to be slower in terms of latency instead. I also would not expect much of a difference performance wise if you access services already using CloudFlare as the endpoints network is likely the same there. However, this is only relevant for your argument of it supposedly being faster. Of course the packets leaving your device are encapsulated and unreadable to third party observers. After being decapsulated its not about routing your VPN traffic anymore but the packets inside which is probably what you were referring to on its own.