The 30-year-old was stretched at times as Preston fought hard in the first half, with midfielder Brad Potts proving a handful on one occasion as he surged onto a slide-rule pass between Matip and Gomez.
When the No. 32 failed to return to the pitch after the interval, there were minor concerns over a fitness issue, though these were swiftly allayed by official club channels.
Klopp addressed his decision during his post-match press conference, explaining that “Joel needs these kind of things,” while emphasising that his replacement deserved his outing.
“Joel is not injured. It was just clear we wanted him to play 45 minutes [so] that he can keep the rhythm – Joel needs these kind of things,” he told reporters.
“It was clear as well that Nat Phillips will come on because we just have to let him out.
“He’s in an incredible shape, is training really well – and I think we could see that. He’s a top-class centre-half and that’s really good to see.”
It is clear that Phillips is fifth choice and will remain that way for the foreseeable future, but his involvement against Preston showed his importance in a long season.
Virgil van Dijk was left out entirely on Wednesday night while Ibrahima Konate was an unused substitute, but with Matip likely to return to the starting lineup against Brighton on Saturday, Phillips was a useful stand-in.
That could be replicated elsewhere throughout the campaign, with Klopp correct in highlighting Phillips as a capable centre-back who can step into the side if needed.
Van Dijk, Matip, Konate and Gomez are as strong a group of centre-backs as at any other side in Europe, but certain games call for a player like Phillips to come in and help preserve their energy.
The goal for Phillips, of course, will be proving Klopp that he is more than that.