The Dodgers starting rotation is in major midseason flux.

A big part of the problem: Bobby Miller is looking like a pitcher lost in the middle.

As a disastrous four-inning, nine-run start in the Dodgers’ 10-1 loss to the Philadelphia Phillies on Tuesday showed, Miller is struggling to find any balance in his game.

He’s stuck between pitches, lacking any reliable secondary weapon to couple with a trademark fastball that remains down a tick or two down from its normal near-triple-digit velocity.

His execution has wavered, looking too intense at some points (leading to overthrows and misses of the strike zone) and too fine at others (dialing back too much in search of better command).

And, in what started as a promising second MLB season for last year’s rookie star, his results have suffered mightily, with Miller now sporting an 8.07 ERA in seven starts this year — not to mention the two-plus months he missed with a shoulder injury.

“I’m a little shell-shocked right now,” manager Dave Roberts said of Miller, who was one of the Dodgers more consistent starters as a rookie last year.

“Given what he’s done, [we were] expecting him to continue to take steps forward and to see where we’re at,” Roberts added. “He’s working his tail off. It’s not about the compete, which I really appreciate. But when you’re trying to get major league hitters out … you gotta make pitches. And that’s the bottom line.”

Miller’s struggles were particularly under the microscope Tuesday.

Before the game, the Dodgers (55-37) placed staff ace Tyler Glasnow on the injured list — making Miller, just 29 starts into his career, the second-most experienced pitcher in a current rotation that includes three rookies.

Then, in the kind of test that could hint towards his October readiness, Miller labored against a potential postseason foe in the Phillies (59-32), enduring a couple of long innings against the majors’ winningest team at Citizens Bank Park.

After retiring five of his first six batters, Miller issued a two-out walk in the second inning to Brandon Marsh, then allowed him to steal second base. Three consecutive singles later, three runs were on the board.

“You face a team like that and you make unexecuted pitches,” a dejected Miller said postgame, “they put good swings on it every time.”

It was the fourth time in seven starts this season Miller has yielded at least three runs in an inning.

It would not be the last such inning of his night, either.

The Phillies — who activated star hitters Bryce Harper and Kyle Schwarber off the injured list Tuesday afternoon — delivered a knockout blow in the fourth.

After a leadoff single from Marsh, Rafael Marchán doubled to left, Johan Rojas looped an RBI single over the third baseman’s head and Schwarber walked to load the bases.

That brought former Dodgers shortstop Trea Turner to the plate.

On a hanging first-pitch slider, he clobbered a grand slam to left field.

That made the score 8-0. A Bryson Stott solo homer later in the frame then pushed the Phillies lead to nine.

“It’s the worst start of my career,” Miller said. “But I’m just glad that’s over with. I’ll bounce back.”

The Dodgers’ offense had plenty of its own troubles against Phillies ace Zach Wheeler, managing just three hits off the All-Star right-hander and no runs until a Cavan Biggio homer in the fifth (Wheeler left the game with back tightness at the start of the sixth).

But, given the state of the team’s banged-up pitching staff, it was Miller’s performance that carried the greatest stakes to the team’s long-term contention plans.

And, on a day their pitching depth got a little thinner, it was his continued struggles that left the biggest cause for alarm.

“I’m trying everything I can,” Miller said. “It’s really tough.”

One theory that both Miller and Roberts shot down postgame: That the pitcher is battling any physical ailments related to his shoulder inflammation earlier this year.

Miller averaged less than 97 mph with his fastball Tuesday for a second consecutive start, something he’d never done previously in his MLB career. He also bemoaned a lack of crispness with his breaking pitches, after striking out just two of the 24 batters he faced.

However, Miller insisted his shoulder felt strong, while Roberts noted that the team’s training staff has identified no physical issues since Miller returned from his injury last month.

“I think it might be more on the delivery side of it, where we can tap into more velocity and commanding of the baseball,” Roberts said.

Whatever the cause, the Dodgers need Miller to find answers fast.

Entering the year, Roberts highlighted Miller as a “big piece of the puzzle” to the Dodgers plans on the mound.

Given their wave of pitching injuries in recent weeks, his importance to the team has only grown.

Unfortunately for the team, so have the frustrations surrounding Miller’s recent struggles.

“It’s certainly a step backward, and it’s a work in progress,” Roberts said. “The psyche part, the confidence, all that stuff has got to be rectified and cleaned up.”

Short hops

Clayton Kershaw will resume his minor-league rehab assignment Saturday with triple A Oklahoma City. That outing will be Kershaw’s first since suffering soreness in his surgically repaired following a start with single A Rancho Cucamonga last month. Kershaw will make at least two minor-league rehab starts in the coming weeks, Roberts said, before the team decides whether he is ready to rejoin the big-league rotation.