This is Dr. David
these are not definite signs of oral or sinus cancer.
I am glad you have shown your dentist the lump on the roof of the mouth.
phlegm in the throat can come from allergies or post nasal drip or acid reflux up the esophagus irritating your throat.
all of this can cause slight swelling of pre auricular lymph nodes.
the most common lump in the roof of the mouth is a benign torus palatinus