The Patriots have been running HOSS Y Juke since at LEAST the Charlie Weis days, if not the Erhardt days. The formations were different each time, but it was the same play, and a play the Patriots have run forever. I would be stunned if Phillips hadn't seen it before.
They had run the personnel grouping before, but never with the spread they used that series. It was reported that not only had they never used this exact formation, they never practiced it.
The formation they ran was to get the Rams personnel on the field to play against the "heavy" formation personnel the Pats had on the field and then force that group to play them in space.
It got more space over the middle for Edelman, and a mismatch for Gronk. If you watch that series again, IIRC, Gronk was much more open the play before his catch than he was when he actually made it. I thought the Rams did a decent job in coverage on that play. But like I have said so many times before, you cannot cover a great throw or a great catch, and on this play it was both.
But if Brady had looked to Gronk the play before, Gronk would have walked in for the TD
As for McDaniel, I'm betting it took him until halftime to figure out exactly what the Rams were doing to be so successful against the Pats offense. He was likely making adjustment the entire 3rd quarter....with little or no success. I'm sure he was getting desperate. I can almost picture him on the sideline at the start of the 4th quarter going, "what if we spread out our heavy personnel against their "big" lineup and see what happens". Then after briefly explaining what he wanted to do the next offensive series he said to Bill, "I know we haven't practiced it, Bill, but I've tried everything else and we haven't done sh! I'll keep it simple, (he ran the same play 4 straight times) lets give it a shot. It SHOULD open up some stuff for us."
"************, Josh", Bill likely replied and stood there thinking about for a few moments, with one eye he watch the Pats defense throttling another Rams offensive series. He couldn't find anything behind the concept that was wrong, but he still didn't like the fact that they had never practiced this formation, not even in a walk thru.
"WTF", he muttered to Josh, but gave him a thumbs up, while Josh was already moving down the bench to where Brady and much of the offense were sitting.
......and the rest is history.