Looking for suggestions on cleaning my stovetop frother. i believe there is calcium buildup preventing full exit of steam from the wand. There are two pressure release valves on the top of the device, both with large slotted heads, can those be opened and cleaned?

I don't know if the release valves can be easily disassembled and re-assembled, I would guess yes.
You could clean it with a solution of vinegar and water. It's pretty effective to remove calcification. Maybe 1 part vinegar to 4 parts water?

It looks like you have hard water, maybe after cleaning, you could switch to distilled water to avoid buildup.

You're on the right track to clean the overpressure valve(s). There used to be a dent in the ceiling of my kitchen where the top of my old steamer had hit it after it blew off the base...