Like to remove a phone from my Simple Choice Family Unlimited Talk and Text plan, but it will not lower by monthly bill

There were a few times when it was available to get a four-line family deal. If you added the fourth line to get one of those deals, then removing the line could actually increase the bill. You could also have some other type of promotion that could fall off if you cancel the line. For example, if you purchased a phone when you added the line and got a promotion to get the phone free, the promotional credits for the phone could stop if you remove the line. 

Those are a couple of possibilities that I can think of without seeing the account. What I would do in your situation is reach out to the T-Force team by sending a message on Facebook or X so they can review the account and see what your options are.