Replaced the wax ring but now it bubbles when the shower runs
You almost certainly have a drain vent problem on the drain to which both the shower and toilet connect.  It could be anything from a clogged vent (most likely if the system was working for a long time and then suddenly started leaking from the toilet flange) to an incorrectly designed stack.

If you want to tackle the problem yourself, you need to understand how vents allow traps and siphons to function properly in a DWV system.