DeffStarr said

Is it possible to involuntary support with the throat whilst "supporting"?

As in, you have the support "locked down" but you're actually supporting from the throat.

I don't know a better way to describe it.

Not in a sense that the neck/throat is tensed up and you feel it there just passively.

During a lesson with Phil, I found it easier to support and produced a supported tone whilst squatting and pushing on the knees with my hands, how you would if you were out of breath and hunched over.

I do find that at times I'm lazy with my support and don't engage it as much as I should and produce very thin tones that become shrill as I get higher. There is also times when i feel the back of my neck tighten as I go higher to compensate.

Should it feel like a down and out motion or in and up?

First question: Yes but it is not the desired end result, it is a step of the process to accept. That dual support kind of thing is a transitory phase some students might go through while they're learning to shift from gripping with the neck to proper support - it becomes especially necessary to take this route if you are performing at the same time as you make this technical adjustment. When the body is shifting from using excess tension (compensatory muscle constriction) to using necessary tension (tensing the correct muscles), in order to sing reliably you will have to allow the two kinds of tension to temporarily overlap for a period of time. It will take loads of effort all over your body up and down just to produce the sound you want. But you should grow out of this in a few months.

When you're not performing or preparing to perform, you can afford to go through the vulnerable phase of having a lack of both excess and necessary tension in that middle point. I'm not a teacher and haven't seen other students go through this - but in my personal experience, I would probably argue that both approaches - relaxed and vulnerable low tension training, and tense and reliable high tension training, eventually helped carve the path to shift from "singing from the throat" to correct support.

Support is a combination of several movements so thinking of it simply as down and out etc. won't work. We're trying to get the diaphragm to stay down, the lower abs go in and up, the solar plexus bulges out but is an expansion tension not a contraction, the sides expand as if opposing being squeezed. I'm not sure what the back does cause I can't see it - I guess I try to think about it being flattened and a grounding anchor for the depth of the breath. CVT actually argues the back tries to tighten and curve - that may be correct as they are correct about a lot of things.

But all of that stuff doesn't make an ounce of sense until you are taught it by a teacher (which I know you have been) and practice it regularly (this may be your weak link)

Another thing is if you ever get sick, keep singing while sick, preferably perform - understand that you will have to support about double or triple the amount you usually do and dive in to that experience - it will improve your support a lot in a very natural way.

Also what Phil says - if you keep on trying even if it sounds bad you'll usually see benefits at the end. Don't shy away once one note sounds or feels wrong.

One last thing, has Phil talked to you about grounding? It's a way of breathing and thinking that's more of a holistic life concept but might help your singing too. I learned it today and it definitely helps in ways that seem relevant to you.