Sounds like some sort of ad popup, which shouldn't be happening really. Not happening on my end, though I do have an ad blocker active. It's even odder that it's happening on a phone...
Is anyone having a popup issue besides lantz?
EDIT: Attempting to research the thing, it looks like some sort of phone app thingie. And typing in the address itself just gives me some sort of weird server sign in pop up. Are you sure it's not a problem with your phone rather than the forum?