also, did I shoot myself in the foot by buying grafted trees?

I just planted a Nam Doc Mai last month that is also grafted, and the graft points on these trees are near the top, unlike some citrus grafts which are under the soil line.

With the colder winters here in Phoenix, would I have been better off getting non grafted variety in case frost ever hits them hard? If the graft points were lower I wouldn't be as worried, but if frost ever hits them obviously the Glenn and Nam Doc portions of the trees will be gone first right?.. Why do they put them so high up on these trees?

I guess I'll just be a very busy guy every winter time erecting frost covers.

Grafted is definitely the way to go.

It's up to you on the rootstock question. As long as that branch is not taking over the tree I think you would be ok letting it grow if you want to eventually try the fruit (may be quite a few years before that branch fruits). Just know that it will make your Glenn portion grow slower. If you are ok with that than it might be fun to try. The manila mangoes are pretty good. You just have to hope it's not on turpentine rootstock.

my Tong Dam from TopT is the same way, the graft is like two feet above the soil line.

maybe it was grafted small like my St Maui and the graft part grew along with the scion?

Is you pic of the right tree? That graft looks pretty low to me?
Also, the graft will not grow higher on the tree as it ages. Tree trunks only grow wider. The hight comes from new growth from the end of the central leader and branch tips.

mango kush,
The rootstock shouldn't grow that much taller along with the scion. They just grafted high.

Why would they graft high? Is there a reasong to graft higher?

Im thinking to prune that rootstock branch then.. I would rather have faster growth on the Glenn..

If I cut the branch will it send the plant into shock.. since its starting to flower will stop flowering?

The main reason i've known nurseries to graft higher is when they have older rootstocks that they either forgot about or the original attempt at budding(or side veneer) did not take so they clefted it later on.

Your plant will be fine if you cut off the branch. It shouldn't stop it from flowering. Don't worry.