You probably ran into me a couple of times cuz i literally main this strat in 1v1 ranked games. There is no real counterstrat to it i guess. Map/division/deck are the factors that decide the game for the allied side. But there are divisions that are better in getting the job done than others (Scots for example).
The idea of that tactic is mainly to abuse the fact that people are mostly more passiv than aggressive. Going +2 in Phase A makes people leave before entering Phase B in 80% of the time. If they stay they are often busy hunting some cheap Infs to balance out the frontline while i take out the troops that are a threat for me.
The biggest problem with this tactic is the lack of AT Guns in phase A. Its not a problem if u know how to manage to play without it doe. If i see support vechicles (churchill/avre) its most of the time no big deal, cuz i dont have to destroy them instantly, i can still push around and force them to retreat. U need to keep in mind i can still bring Stugs/Schrecks/Henschel. You need air superiority or at least to be able to stop henschels, wich are (at least for me) vital.
I dont recomment u to try to spam Bombers/Arty. Its not worth bombing down troops that cost me absolutely nothing. If some Inf gets pinned down by arty i can instant reatreat them and send them forward again.
The games i lose are mostly managed by a healthy coutnerspam of inf aswell as well placed supports and a won air war, what prevents me of bringing in henschels.
so what i am afraid of is
+counterspam of cheap inf
+well placed supports snipers/churchs/flammers
+some numbers of med tank (shermans for example)
+good use of anti-air units
what i laugh about is
-spam of bombers/arty
-light vehicle spam
-elite inf spam
-tank spam especially heavy tanks
Try to grind the down the inf and holding the frontline. Some Players for example managed to grind my complete Army down and go +3 but it was to late, cuz they did a good job on the tactical side, but not keeping the time in mind. So i won the game and did literally nothing anymore the rest of the match and still won the game cuz i early on had map advantage. Some others pushed to hard so i grinded them down instead until they left in Phase B (often seen by 101st players with elite inf spams). you need to find the balance and u will win every game against this strat.