Because we can’t control the vocal folds by feel very well (perhaps not at all), it can be hard to know how much air pressure is being pushed at them from below. It probably varies a good amount in different people at different times, especially given the different bulk of people’s folds, and the strength therein to resist the subglottal air pressure.
The physiological truth of the larynx is that it does function as a valve, but not always with the same setting. The glottis closes to prevent foreign bodies from invading the lungs, to cough, to stabilize air pressure in the body during heavy lifting, and lastly, but by far most gently, to make sound. The difference between singing and those other activities is that a very, very small stream of air must pass through the glottis in a smooth and sustained manner in order to make the vibrations for vocalization. That requires a delicate balance between flow and closure. Very!
Do we go by what we feel, or what’s real? I believe that for most people, if you feel the throat holding back air, you are pushing too hard and holding the “valve” too tightly closed. A more useful feeling of “holding back” might be with the rib cage or the whole torso, or a generalized feeling of keeping the inhalation muscles engaged while making sound. Some people find it useful to think of things other than physiological reality: things like “drinking in the tone”, “inalare la voce (inhale the voice)”, “gathering in/concentrating the sound”, and the like. I found Craig Shimizu’s explanation of the helpfulness of such concepts interesting.
If you feel actual pressure in your throat, you are probably working too hard, with excessive tension. The larynx, which can be called a valve, needs to not feel like a valve. It needs to be treated gently, not squeezed and pushed. Ironically this calls for general muscle tone and strength in the body in order to find that balance. Learning how to grow the sound without pushing leads to breakthroughs in endurance, flexibility, freedom of expression, and generally sounding better!