

I settled on https://www.audiobookshelf.org Might be a bit confusing at first, but after setting it up, it does exactly what I want. Easy to listen to podcast on my iPhone, including setting speed & sleep timer and the server fetches the new episodes every day.
There is NextCloud. It has the possibility to create an upload link where people can upload stuff. We use it daily to receive stuff from our customers.
If you need the resuming part, you would be better off giving them a NextCloud account and share a folder. Their NextCloud app will sync it in the background and resume automatically.