Thankfully that horseshit was debunked a while ago, the guy who normally posts those rumours confirmed and proved it wasn't his account.
I do wonder if a time aspect will be involved, since I'm assuming every Phase 3 film will involve some Infinity Stone. But that was way overboard.
Every Phase 3 film? Eh, I honestly really doubt it. Remember, by the end of GotG we'll have established three of the stones (I'm assuming that Captain America 2 won't establish one) and their whereabouts. That means that only three of the Phase 3 films need to introduce any new ones, and there'll likely be more than three films between Avengers 2 and Avengers 3.
If they want to go as far as introducing the Negative Zone in Ant-Man, then sure, they could find an Infinity Stone there. But I think that other films are probably more likely to result in that stuff (Dr. Strange is virtually a lock for introducing an Infinity Stone, I think).
We're supposed to hear more about MCU Phase 3, including confirmation of which films will be coming out in 2016, sometime in the next few months, if I recall correctly. They've already locked down May 5, 2016 and July 8, 2016 for unknown films, as well as May 6, 2017. But I think they're trying to do their best to make sure that they don't need to shoehorn an Infinity Stone Macguffin into every single MCU film leading up to Phase 3. Just, you know, some of them.