Jesse Tyler Ferguson is hearing voices in his head. Lots of them. But that’s the risk you take when you tackle Becky Mode’s “Fully Committed,” a raucous comedy and one-man show opening at the Lyceum Theatre on Sunday, April 24.

Talk about a star turn . . . and turn . . . and turn. Ferguson plays Sam, a struggling actor working the reservations line at an uber-trendy Manhattan restaurant (the kind of place that serves crispy deer lichen dusted with edible dirt). He also plays the egocentric chef, a French maitre d’, flustered East London hostess, plus an array of callers, from Gwyneth Paltrow’s detail-obsessed assistant to an increasingly apoplectic Upper East Side socialite (“This is Carolann Rosenstein-Fishburn calling for the third time!!”), even a Time Warner Cable robocall — 40 characters in all.

Ferguson, 40, the lovably uptight Mitchell Pritchett on ABC’s “Modern Family,” made his Broadway debut as Leaf Coneybear in 2005’s “The 25th Annual Putnam County Spelling Bee,” and was most recently seen in last year’s Central Park production of “The Tempest.” He spoke to Newsday contributor Joseph V. Amodio by phone in between sets at the gym.

How’s the workout going?

In this show my body is in full motion for 90 minutes — so staying fit and keeping my cardio up has been helpful.

Yeah, this show is a physical workout as much as a vocal one. Did you base the voices on real people?

A lot of them. The script gives you some goal posts — like the maitre d’ is French. But the playwright was open to my ideas. When my character calls his agent’s office — the assistant there is based on Tim Gunn. I just think he’s such a nurturing person on “Project Runway” — and he has a fun voice. Bob from the office is based on Richard Kind. We were in “The Producers” at the Hollywood Bowl. And Bunny Vandevere is based on Jeannine Pirro.

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The former Westchester DA?

I was watching the documentary “The Jinx” . . .

Oh . . . about Robert Durst, who’s accused of murdering his wife.

Jeannine Pirro was trying to prosecute this guy, and she had this wonderful, tight-lipped way of speaking.

Then there’s Gwyneth Paltrow’s assistant, with all the wacky demands. Hilarious.

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We added that about a week before getting to the theater. When the play was originally performed (Off Broadway in 1999), it was written as Naomi Campbell’s assistant. And she’s perfectly relevant today. But we thought Gwyneth might strike a chord, and it seems to be working so we kept it.

Have there been many changes?

Some. The playwright was much younger when she wrote this. She has kids now, and wanted to bring more of that emotion into the story with the relationship of Sam and his father. So that’s fleshed out. It’s great — like working on a new play.

Forty voices — plusscript changes. Ever gotten lost?

Only once in performance, and a lot of people said they didn’t notice. My stage manager piped in, reminded me where I was, and I got back on track. When we change the script, I have little Post-it notes on my desk with key words to remind me what the line might be. They disappear as I get comfortable with the changes. But . . . (he chuckles) there was a time when my desk was covered with notes. I’d look down and wouldn’t know which to look at. It’s like muscle memory. While you’re in the moment of what you’re playing, your brain has to think ahead to what’s coming next. I’ve never had to work this way. You always want to be completely invested in the moment and let your scene partner . . . bring you to the next moment. But I am my own scene partner, so I have to be on my toes in a way I’ve never had to be before.

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This is a far cry from a day on the set of “Modern Family.”

For sure. That’s such an ensemble piece. Each episode runs about 22 minutes, with commercials — if you timed out how much screen time each of us had it would be about six or seven minutes per episode. Here I’m doing 90 minutes and every character. (“Modern Family” co-star) Ty Burrell, he’s a theater veteran — he’s impressed I’m doing this. And (co-star) Eric Stonestreet has always wanted to do theater — he’d be great onstage. They’re all extremely supportive.

In the play, you do an impression of one member of the “Modern Family” cast.

Yeah, and I don’t wanna ruin it, because it’s a fun surprise. But, yes, there’s a cameo some people might recognize.

Has “that person” seen this yet?

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Not yet, no. But “that person” will. Soon. That’s why I want to keep it a surprise. It pops up out of nowhere. And it’s been getting a fantastic response.