Q.Fiddle leaf Philodendrons – Large root bound in container
I have a large 2.5-3′ wide Fiddle leaf Philodendron in an outdoor container. The pot curves in at the top and either I break the pot or cut the plant out. My question is will it kill the plant if we cut the rootball down about 3″ all the way around to get it out? Or should we break the pot?

I would suggest watering the plant well and enlisting the help of a few other people.
You should be able to set the pot on it's side and work the plant out of the pot.
If your not able to free the plant by sliding out the root ball, you can then gently break the pot and free the entire root ball.
Some pruning of the roots could be done, but not as drastic as you mention.
I suspect your roots are quite tight in the pot and can be gently opened up.
Use a good quality potting soil and a pot that adequately holds the root ball with a bit more room. Make sure it has a good drainage hole or two.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/types-of-potting-soil.htm
The yellowing leaves may be due to lack of moisture, the soil may not be holding enough moisture with it root bound.