Malphite is a tank, so why is he actually good against Gwen in lane?

If Gwen just uses her QWE combo and pops her Hallowed Mist, it feels like Malphite can't do shit and would just run out of mana. Even if Malphite ults in, Gwen should be able to just go "is this guy crazy?" and beat the hell out of him, but somehow Malphite has the edge in lane lol