The League One side looked a class above the Mariners in a largely dominant first half and they took the lead just before the half-hour with a header from the former striker Sunderland Connor Wickham.
But there was a noticeable improvement after half-time as Phillips’ men showed greater enthusiasm and produced more quality moments to start putting their visitors under serious pressure for the first time in the contest.
Michael Woods and Dillon Morse both went close with headers within ten minutes of the restart and Blair Adams hit the side netting with an oblique drive after earning a superb cross pass from Martin Smith.
Mackenzie Heaney curled a free-kick just wide of the target heading into the closing stages and there was almost a superb equalizer from defender Tom Broadbent as he dipped just beyond the far post as the game progressed into additional time.
The visitors delivered the decisive blow moments later when Wickham stunned the 1st Cloud Arena with a brilliant long-range effort to see his side through and let Phillips and the Mariners focus on Tuesday night’s crucial home clash with league leaders Hyde United.
Speaking after the match, the Mariners boss told The Gazette: “An FA Cup run can help (a league title bid) but it can hinder.
“Hyde United will come here looking to jump on the disappointment so I can’t afford that to happen. I told the players, yes you are disappointed but when you wake up tomorrow morning the focus is put on tuesday.
“We’re desperate to get out of this league and I said if they play like they did in the second half for the rest of the season we should win the league. We know we’re not going to play like this every game, but we continue.
“We will score goals and I can’t stress enough how proud I am of these players.”
Phillips explained the reasons behind his side’s subdued performance in the first half as they looked to contain a spirited Forest Green side.
The Mariners boss revealed his team’s much improved second-half display was the result of some talk in the home dressing room during the interval and praised his players for making life uncomfortable for the team. Ian Burchnall after the interval.
“Sometimes you can’t start with enthusiasm because good teams will pass it on to you. We showed a little too much respect in the first half, but they never really opened up to us every time.
“Yes, they had a lot of ball possession and scored, from our perspective, a soft goal after a cross, but we knew we could get to half time, come in, discuss and adjust, increase the pressure and say that we would not leave the field with regrets.
South Shields: Boney, Newton, Broadbent, Liddle, Morse (Briggs), Smith, Mottley-Henry, Woods, Alessandra (Hunter), Heaney, Adams Subs: Doherty, Dobson, Gomes, Ross, Marriott, HodgsonForest Green Rovers: Thomas, O’Keefe, Bernard, Casey, Cargill, Boyes, Hendry (McAllister), Bunker, Little, Whickham, Matt (Mars) Subs: McGee, Marques, Robertson, Peart-Harris, O’Brien, Fiabema