The attitude of the pupil, in singing, should be as natural and easy as possible.Mathilde Marchesi, Bel Canto: A theoretical & practical vocal method. Dover Publications, Inc., New York.
The image above says it all.
Here are two audio examples to demonstrate the importance of the neck position for singing.
Example one demonstrates a note that is distorted by sticking my neck out. I begin the note in a noble posture. I then stick my neck out as if I am looking at my iPhone. I then resume the noble posture. I repeat this. Listen to the sound deteriorate. I change nothing except my neck position!
Example two demonstrates scales to a top C. As the scale went higher I adjusted my neck position to enable more length in the back of my neck. (I trained myself to lengthen my neck by grabbing my pigtail and pulling it upwards. Good luck with using this training method in today’s world).
Here is a link to a previous post of mine for more information about this diagram above. I use Oskar Guttmann’s exercises every day for about six minutes before I vocalise. His 19th Century book is freely available on the internet. https://deborahwaikapohe.com/2020/03/22/oskar-guttmanns-breathing-exercises/
As an aside, here is a post from osteopath.net.nz to assist if the phone has got the better of your neck position. https://www.osteopath.net.nz/blog/text-neck-how-looking-down-at-your-mobile-phone-can-strain-your-neck/