I want to at least read sensors and maybe control a grain dryer via cell phone

I was wondering if I could even do this.... We own a grain dryer company and we use type J thermocouples for measuring the temp of the dryer. I found a type J them sheild online that appears to be able to mount to the UNO R3. also I was hoping I could stack a Arduino GSM sheild in there as well. New to Arduino so this is an ambitious project for me. Was wondering if this could be done in a way where I still have some inputs and outputs left to be able to measure some more things like the moisture of the grain and then maybe be able to control the already existing metering control of the grain flow which control the speed of the unloading grain. Would be nice if all of this could be done from a cell phone. Any thoughts??

Certainly doable. But as you said, a ambitious project. Also, using shields can complicate things since many of them force you to use certain pins. In some cases this is no issue since for example spi pins are designated by hardware but in other cases it might cause conflicts.
What temperature range do you want to measure? And with what precision? There might be other sensors that can do the job with grater flexibility.

A few months ago there was someone else here asking a similar question about grain hoppers and dryers. I suggest you search this site first and then Google for 'grain hopper arduino'.