The pair played alongside each other for the whole of last Saturday’s 1-0 home Championship defeat by Sheffield Wednesday.
And 82 minutes into Tuesday’s 3-0 loss at Middlesbrough, Whitehead made way for the Danish teenager.
Billing, fresh from signing a new Town contract through to 2020, is getting solid game time under head coach David Wagner.
The 2013 signing from Esbjerg is hoping for an eighth start, and 13th appearance in all, at home to Hull City.
Wagner terms the 6ft 5in 19-year-old “a talent and a good character who is football intelligent”.
And the vastly experienced Whitehead said: “He’ll get better and better the more games he plays.
“Players with all the attributes can go as high as they want and he has all the attributes.”
Whitehead says the older heads in the Town dressing room back the younger ones all the way, helping their development.
He added: “All the older lads will get round Phil and make sure he does the right things on and off the field.
“He has to keep working hard every day and try and improve and not take his foot off the pedal.
“I am sure the manager here will drill that into him and make him a better player in all areas.”
Billing, a towering presence at 6ft 5in tall, produced a great penalty-area tackle to thwart Wednesday’s Aiden McGeady.
Whitehead enthused: “It was a great tackle and I don’t think a player without his long legs could have reached it!
“It had to be perfectly timed, too, as it was just inside the box. That shows what he is capable of.”