Leeds head coach Thomas Christiansen identified Phillips as a box-to-box star in the making after taking over in pre-season but felt he needed to shed a few pounds.
The 20-year-old took his advice on board, and said: “I feel like I’ve improved a lot.
“Physically I’m quite big so I’ve got quite a bit of body fat. He tried to make me slim down so I could be quicker and a little bit sharper.
“It’s hard because you love a chocolate cake after Sunday dinner but you’ve got to nip these things in the bud. I’ve started eating a lot healthier.
“In the first couple of weeks I felt a bit drained but by cutting down on certain things I’ve felt the benefit. You can see that in my performances.”
Leeds have lost seven of their nine games to slide down the Championship table.
Question marks have subsequently been raised about Christiansen, but Phillips said: “Obviously you feel for him because he’s working as hard as he can to get the results we need.
“I just think the last few games have been about little lapses in concentration.
GETTY
Leeds boss Thomas Christiansen told Kalvin Phillips to slim down
“At Brentford I thought we were the better team throughout the second half. We looked like we were going to win it and it was lapses of concentration that cost us.
“In the Championship if you lose concentration the opposition score goals. I’ve said it about five times now but we’ve got to cut it out.
“We all believe in (Christiansen). From the get-go we started very well this season, after what he’d worked on in pre-season. This is a bad run of results now but we have to keep pushing.”
Leeds fans have been alarmed by their woeful form, which has seen them drop from the top of the table to 10th.
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A section of supporters have criticised the flurry of foreign signings brought to the club by director of football Victor Orta but Phillips believes there is no need to panic.
“We take it on the chin and we know we’ve had a couple of bad results but sometimes people over-exaggerate a little bit,” he said.
“It’s a bad run of games but if we’d started with a bad run of games and then gone on the run we had at the beginning of the season, everyone would be happy. It’s football and it’s the kind of thing people look at. We can’t let it get to us.
“I’m always confident. There’s no point being down about stuff because there are a lot bigger things outside of football that people are going through. Being confident gives you a chance of being a better player.”
Leeds chiefs are targeting a play-off finish and when asked whether promotion was a realistic aim under Christiansen, Phillips said: “That’s our goal. We won’t any less than that and if we do we’ll be very, very disappointed, but we’ve got enough talent to be in the top six.”