United head to the Nou Camp 1-0 down going into the second leg of their Champions League quarter-final.
The Red Devils are back in the city 20 years on from beating Bayern Munich at the famous stadium in the 1999 Champions League final.
That earned Manchester United the treble with current boss Ole Gunnar Solskjaer scoring a last-gasp winner.
And Phelan wants United fans to be just as loud tonight as they were two decades ago.
Phelan tweeted alongside a picture of the area between the tunnel and the pitch: “Nothing better than an away day in Europe with #ManUnited.
“Morning all, enjoy the day and make some noise.. This is the one”
Manchester United go into the clash with Barcelona with plenty of news ahead of the match:
But Red Devils fans want the famous final to inspire their club tonight.
One responded to Phelan: “Good luck remember 99”
Another added: “Noise Mr Phelan if we have are way the win n the world will hear the war cry of the red devils loud and proud give us another night to remember”
A third wrote: “Gwaan Mike! You and the team can make us dream again. We know you can do this.”
And a fellow United fan said: “Can we go back to 99 today!”
While one more added: “Make it another great night to remember”
United upset the odds to comeback against PSG in the round of 16. And Solskjaer wants his side to take inspiration from that game rather than 20 years ago.
Asked whether he will speak to his players about 1999, the Norwegian said: “No I won’t because it was against Bayern Munich, it was a final, it was different.
“We will use the PSG (match), we will use Juventus away, we have beaten some good teams away from home this year, and played against some great players.
“We had (Barcelona) flustered at times here [in first leg] as well.
“Yes, they controlled the game towards the end, they had the possession but they never really bothered us in our own half.”