Looks hungry

You can even see the webbing. To get rid of the mites spray with a miticide, of just spray the tree (upper leaf, lower leaf and trunk) with a forceful spray from the hose. As bad as the condition is I would throughly spray the tree 3 or 4 times on successive days.

Wow that is a really bad infestation of mites im surprised the leaves haven’t fallen off yet but yes to all the above spray spray spray and ASAP too!!

And, as Jim said, it needs many low doses of liquid fertilizer fast.

Check for scale as well on stems and leaf stems. Yes Spider mites are nasty; Fertilizer will help with the next set of leaves that come out. I would clean it up and possibly remove the leaves that are left and let it start fresh.

If you want to remove the discolored leaves, I would wait until the new leaves develop. Note that new citrus leaves do not begain to produce food for a tree until they become fully developed.