Answer answer the fact that there is a squeak under the tile suggests that the wood underlayment subfloor is moving to some degree.
Floor creaks under toilet.
You may need to scrape the flange with a small putty knife and use a wire brush to get it clean and free of any corrosion or debris.
The bucket will catch any water that may be trapped in this area.
Repair floor under toilet nail the plywood to the floor joists.
You may not think of your floor as vulnerable but in the bathroom it is.
Normally this is avoided if when the wood subfloor underlayment is installed it is glued and screwed so there isn t any movement or chance for there.
A spongy floor around the toilet is a strong indication that the subfloor has absorbed water.
Clean the flange well or use a new one and install over the drain and new wood.
Remove enough of the drywall to open the area under the shower and toilet.
Rather than tear into the finished floor i suggest that you start in the basement ceiling where the soft spot is located.
With some effort you can slide them back tight again.
Peel back the flooring around the fixture and you will.
Make sure to make your nails flush with the wood.
How to fix a rotten floor around the toilet.
Around the toilet the floor may get flooded from overflowing.
How to replace a rotten floor in front of a bathtub.