The manager famed for meticulous preparation flipped at the prospect of losing Phillips - and several other Leeds stars - for ten days of their build up to facing Liverpool on Saturday.
The idea his plans for the Yorkshire club’s much-anticipated return to the elite were being disrupted by Gareth Southgate did not go down well.
Initially, that is.
For, once his irritation subsided, Bielsa’s mood changed to one of pride as he gave Phillips his blessing to join up with England – and handed him an old club shirt from his playing days in Argentina, along with a written message.
Phillips, 24, who until now had never been picked at any Three Lions level, said: “The manager was pulling his hair out because quite a few lads were going off to internationals.
“He was thinking he didn’t have enough time to prepare for Liverpool who, obviously, are the champions.
“But once he settled down he gave me a gift – a replica Newell’s Old Boys black and red top. I’m going to get it signed, framed and put it up at home.
“There was a note as well. It said: ‘The hard work has paid off but it doesn’t stop here’ - and that he was happy for me, my grandma, mum and girlfriend.
“It was a really nice touch.”
If anything encapsulates the South American coach, considered by many, including Pep Guardiola’, to be the most innovative on the planet, this episode does it.
Deemed a tad mad when it comes to his 24/7 training methods, Bielsa, 65, clearly possesses a softer, humane side that outsiders rarely see.
The fact Phillips has promised to give his first England shirt to the Elland Road supremo - as a reciprocal thank you - underlines the bond between Bielsa and his Premier League rookies.
Phillips, whose conversion under Bielsa from rampaging midfielder to ball-playing anchorman has resulted in his elevation into Southgate’s set-up, knows how much he owes the ex-Argentina and Chile boss.
“I’m giving my shirt to Marcelo, as a trade. Everyone has a view of him and they don’t really know him,” explained the Leeds-born ace.
“He’s obsessed with football and making players the best he can. He’s done that with me in two years.
“I was surprised when he switched me from a box-to-box midfielder. But I was never going to say no because of his reputation.
“It took a good six or seven months to get used to it and learn the role, where to get the ball, where not, and to work on the defensive side.
“I think Marcelo is relieved to see his work is paying off.”
Hard to dispute that, given on Tuesday, Phillips, who also qualifies for Jamaica, could fulfil his Three Lions dream.
Come Saturday, he should be at Anfield for his top-flight debut.
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As for those vital missed sessions with Bielsa, all is not lost as the Leeds backroom team have been in contact over the past week.
Phillips, with 12 goals in 165 league games for the club, said: “Marcelo is not sending messages but his staff reach out to us, ask what work we’re doing, if we feel we’re working hard and being worked hard enough.”
The relentless attention to detail never stops.