Phone volume

Phone volume automatically lowers while listening to podcasts through the phones speakers.
It will do this several times while listening to any podcast through AntennaPod.

AntennaPod doesn’t adjust the phone volume, apart from boosting or lowering the volume of specific podcasts if you have set it for those podcasts. But so the volume should change only between episodes, not within an episode (which seems different from what you’re describing), and only if you have manually changed the podcast settings.

I know that on my previous phone Android automatically lowered volume after a while when listening through earplugs, to protect the ears. Maybe your phone has something like that as well.

I would do a web search (Google, DuckDuckGo, etc) for your phone model and the problem – maybe others have experienced similar issues.